The only situation where someone might return a chip after 7 months or 2 years (with appropriate documentation) is if a chip was sole as real and turns out to be a fake. Or if it's sold as Las Vegas and turns out to be a CA cardroon or something. In other words sold as one chip, when it's another.

Otherwise, if I buy chip "X" from you and six months later someone finds a box of them. Gee Wiz, tough luck for me.

Imagine if I have a chip I bought two years ago and now I find out I paid too much for it, in my opinion, I can return it? I don't think so.

Unless there are some missing details, like the chip isn't from where you said or isn't what you said it was, 30 days sounds fair enough in my opinion.