I have two sixes and love 'em.
That's a suspiciously good price. Check it thoroughly. Check for weakness in the winder, a clean battery area, non-corroded contacts, securely deploying collapse mechanism (you really should try it with a lens on): it should find both positions (in and out) securely and with conviction! There is indeed a large, black button (lower right of the lens as you face it) which allows the collapse mechanism to release. Make sure that works; the 6 was discontinued largely because of issues with that particular mechanism, and I am not sure how readily it can be fixed if there is an issue. Worst case, we might have to think of how to secure it in the "out" position, permanently.
Ideally you would (with a lens on) open up the back, set the timer on B, and fire and wind a few times and make sure everything is good to go. Also check the curtain feature (which protects film during lens swaps or lens during film swaps). This is controlled via the pac-man button on the bottom.
If you want to send it over I can have a good look with a lens, but I am deinfitely not able to CLA, all I can do is tell you if it's working properly and make minor adjustments. So you could just as well send it to KEH for a check-up and say that you'll buy a lens if they will check it out. They have a very good return policy and would give you a buying discount if you turn it in as ugly/bargain....
Anyway $250 is a really good price if it is indeed shootable
Good news is that all the timing intricacies are in the lenses, so at least you don't have to sweat that. Worst case you'll buy a lens and discover you need another body. I have seen them go for $500 or so. In that case, it's a win-win situation, because you'd have a "parts" body in case you have a winder failure or whatever.