(This is a work in progress, I'll update this post in the future.)

Nintendo 3DS testing cheat sheet:

So you don't forget the steps while testing. Elaboration and more info below.

1. Check the outside: Make sure it matches the price you're being asked to pay. Do not buy a 3DS with a cracked hinge. Trust me, you'll find another model without crack, be patient. The crack always gets worse, you'd have to replace the entire housing, it's simply not worth it.
2. Check for CFW: Hold Select when turning on the console. If it shows the Luma screen, it's hacked. If it boots to the normal 3DS home screen, it's not hacked.
3. Buttons: Shoulder buttons, thumbstick(s), ABXY, Start, Select and Home are working.
4. Speaker and 3D slider: Slide up and down, see if both functions work. Make sure the sliders stay in position and don't move involuntarily and aren't too tight either.
5. Battery and charger: Check for visible and palpable bulging of the back cover. If you brought a screw driver: Take out the battery, lay it on a flat surface and give it a spin. If it continues spinning like a beyblade, the battery is swollen = bad. If the battery is swollen, don't try to charge it. If it's good, plug it in and see if charging works. If it doesn't, I wouldn't buy (worst case it's the charging port). If you encountered worn out screws - I personally wouldn't buy.
6. Touch Screen and Stylus: Test every corner of the touch screen. Check if the stylus is original from Nintendo (replicas often have sharp edges).
7. Cartridge: Bring your own game, or ask the seller to bring one. Insert the cartridge, the game icon should show up on the home screen. If it doesn't, maybe try with a second game. If both don't work, the game reader might be faulty.
8. Flex cable stress test: Move the upper screen a little bit while the 3DS is powered on. When the flex cable of the screen has an issue, moving around the upper screen often leads to the 3DS shutting down with a pop noise from the speakers = bad.
9. Parental control and software version: Go to system settings and check the parental controls. If they're active, ask for a pin. If the seller doesn't have the pin and the software version is v11.16 or older, it can be removed using a website (emphasis on *can*, maybe the website gets taken down, maybe it just doesn't work for whatever reason). If it's 11.17 or newer and the seller has no pin = bad. It's best to get the pin from the seller.Regarding firmware version and hacking: As I'm writing this, hacking is possible with the newest firmware. That can always change when there's a new update, keep that in mind.
10. Test the internet function: Log into the nearest WiFI to make sure it works

What to look out for and consider

The different models:

There are several different DS and 3DS models. If you want to buy a Nintendo 3DS, make sure it has at least one thumbstick. The DS only has the d-pad. The 3DS slider is not an indicator, as the Nintendo 2DS and Nintendo 2DS XL are missing the slider and 3D function, but are part of the 3DS family (weird, I know). The New models (New Nintendo 2DS XL, New Nintendo 3DS, New Nintendo 3DS XL) all have a second smaller thumbstick on the right side of the console. That's how you generally tell them apart.

They all have their advantages and disadvantages, most importantly: The 2DS XL is hard to repair, the 2DS is robust and probably best for kids and anger issues, the old 3DS XL has the most fragile hinge, the New 3DS (no XL) has a unique battery capacity which sucks to find online.

Whether or not the console is hacked

There's nothing wrong with a hacked console per se, unless the previous owner didn't know what they were doing and messed up the files. I personally like to be on the safe side and hack myself and don't buy hacked consoles. It's possible to fix a hacked console with issues, but I find it's a pain in the ass and easier to hack myself. Just something to consider. If you'd rather have a console that isn't hacked, test it by holding the select button while powering it on. If it boots to the normal home screen, it isn't hacked. If you see a black screen with red and white letters saying something about Luma, it's hacked.

A console might be hacked and region swapped. Careful with those, because you won't be able to remove the CFW without undoing the region swap first, or else you'll brick the 3DS. If it's hacked and in a language that it's not supposed to be, it's region swapped.

Function of the battery and charger

Sometimes it's not practical to bring a screw driver (Phillips #00), but I would always recommend it. Not only can you test, if the screws are worn out (bad), but you can check the state of the battery. I already mentioned above how to test it, but I just want to stress again how important this step is. Not only is a swollen battery dangerous, it can be pretty annoying to find a replacement for some models.

It's especially annoying for the New Nintendo 3DS (not XL), because the replacement batteries for this model all have a lower capacity than the original, even if it says the right capacity on the battery. The original ones for this model are extremely rare and to me personally a swollen battery in this one would be a reason to decide against buying . It's also annoying for the New Nintendo 2DS XL, because that one is just annoying to open.

The rest are fairly easy to replace. But for safety reasons I'd still check. You should also consider paying less for a console with a swollen or dead battery, because you'll have to pay for a replacement.

Function of buttons and sliders

Make sure to really test all the buttons, sliders and sticks. You can test the two shoulder buttons on the home screen (should make a little bar pop up in the bottom of the top screen). I'll play around with my 3DS and update this post with easy methods to test all the other buttons. Shoulder and ABXY buttons are fairly easy to replace on the old 3DS consoles, more tricky on the new ones. With fairly easy I mean for someone who has repaired small devices like a 3DS before, still hard and finicky for someone who hasn't done it before. I personally don't bother with repairing a 2DS XL.

The left slider controls the volume, that's self explanatory, the right slider controls 3D (not on the 2DS models). When sliding that one up, you should see the 3D effect on the upper screen.

When checking the thumbsticks, check to see if the left one has a rubber cap that's securely on there and not brittle. There are NO replacements for that rupper cap, only replacements for the entire stick and they don't have a separate cap attached to the stick, just a rubbery surface on the plastic stick. Some people don't mind, I personally hate the replacement sticks sold online. So, it's worth checking.

Screens

I'd say 90% of the issues where a 3DS turns itself off without warning are related to the upper screen (in my experience). The 3DS turns itself off, when a flex cable is defective or not attached properly. In some cases it might be the flex cable of the sliders, but in most cases it's the upper screen. It's worth testing for this issue (like I said above, move the upper screen a little bit, open the 3DS all the way, close it half way, etc. while it's turned on), because replacing the upper screen is very difficult and finicky, even for someone experienced. It's incredibly easy to ruin the fragile flex cables, especially in the New models, where the cable is threaded through the hinge. So if the screen flickers or the 3DS shuts off, it's better not to buy.

It's easier to replace the touch screen, but still tricky for someone inexperienced. If the 3DS only has a replicated stylus, you should absolutely get a screen protector for you touch screen. All of the 3rd party stylus I have come across, have a sharp little edge somewhere and I personaly wouldn't want my screens scratched.

IPS screens:

Some new models have an IPS screen. You recognize those when looking at them from an angle and still getting a bright and sharp image, like when looking at them head on. Regular screens look a bit "washed out" when looking at them from the side.

The IPS screens are sought after because they are "rare" (not really, there's a shit ton of them). Yes, it's cool that you get a sharper image when looking at them from the side. But nobody plays like that, we all face our 3DS from the front when playing. Why, do you think, do people always post a side by side comparison with a normal screen 3DS and showing them from an angle? It's because most people simply couldn't tell just by looking at it from the front. Is it kinda cool when you find out you have one of those? Sure. Worth the extremely steep price? Absolutely not.

Japanese Retro Videogame Console Buying Guide

from u/SteveW_MC

The best ways to find a 3DS

from u/notthegoatseguy

The Nintendo 3DS family of systems was discontinued by Nintendo in early 2020. The 3DS family of systems is no longer being stocked by standard retail stores from orders with Nintendo. But individual sellers and used/secondhand businesses may sell them on the secondhand market.

The bet ways to find them:

• eBay has been in business for 20+ years and guarantees that you will get the item as described or your money back. The catch is you need to read the full listing to understand what you are ordering. You can also consult reviews of the seller and ask the seller further questions. Despite its reputation as an auction site, most transactions are regular purchases nowadays
• Amazon/Amazon Japan: Listings are up and individual sellers will sell them on the listings. Check reviews. If shipped by Amazon or fulfilled, Amazon will have your back and it qualifies for their return policy. You can also look at Amazon Japan for importing a system, though your country may have import taxes associated with imports.
• Your local game store
• The popular buy/sell app people in your local area use to buy and sell things such as Facebook Marketplace, Craigslist, and Kijiji are some more popular examples.
• r/gamesale.

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