Does this Samsung Nexus S seem fixable?

Should be, but hard to know for certain. For the right price, probably worth a shot. See the video below for how to unroot/unbrick/put the phone back to stock.

Good news about Samsung phones is they're very hard to truly brick the device. If you have more questions, QBKing77 on youtube would be the best person to ask, he's great with helping people like this

How to unroot the Nexus S 4G back to stock Android 2.3.5 - YouTube

 

It actually should be quite easy. I'm betting they just flashed an unstable rom, there are a few that will break WiFi.

As long as you can flash a custom recovery and boots up just fine. You can easily just download a new rom and flash it in recovery.

The only thing I would worry about is buying a defective device. You won't know if it will be the device or the software until you try flashing a new rom, and possibly radio.

I wouldn't suggest paying for it unless you have a way to return it, if it is the device.

 

I'm not sure, honestly don't know too much about the Nexus. If you have a Google/youtube account, you can click on his name and go to his channel, then click where it says "send message" and you should be able to contact him on youtube.

One thing to make sure you do, contact the carrier and make sure the ESN is clean and clear before buying the device.

 

Yes the hardware could simply be broken. So you should be skeptical dealing with a private seller. I believe the warranty is no longer valid if it's resold.

That is a very reasonable price for it, but if the WiFi is broken you may end up spending quite a bit just to fix it.

The tutorial that was posted will only work for the Nexus S 4G. It's pretty similar to the instructions for the i9020 or i9023, Although it would be extremely confusing since they use different radios. But I would be happy to find you one that will work for another version.

Edit: here's a good one.

www.theunlockr.com/2011/01/20/how-to-unroot-the-nexus-s/

 

The tutorial will still work even though they are a little old. You don't need to worry about backing anything up. You could wipe data + sd card and be fine. As long as you can still place a rom on your sd card afterwards.

If they say it's a "clear mod" and can't give you any details on the specific rom they probably shouldn't even have rooted the device in the first place. Lol.

It's not possible to tell if the WiFi is broken without flashing a new rom or restoring to stock. Since the ROM they flashed could have disabled the WiFi, or something is causing it to not work. But if you were to flash a stable rom you could instantly tell if it's the hardware or software.

If you do end up making the purchase, feel free to send me a PM with any help/rooting questions. I switch roms and kernels pretty frequently on my Nexus S.

If you aren't very familiar with rooting this may be more of a hassle than it's worth. But it sounds like you are pretty knowledgeable, and might be able to handle it pretty well.