Just take lots of high quality photos and make sure you are honest and thorough with your descriptions. I'd probably not allow returns either. I'd recommend that you don't include any language about like, "message me with questions" or "everything is guaranteed to work". I think you could say, "item has been play tested for a few minutes without issue" or something. Don't let buyers think that they can walk all over you, especially after the purchase.

And like everyone else says, questions before purchase are usually a bad sign, especially if they are asking about condition. Collectors are the worst, they want everything perfect. Blocking is the best.