I think the buyer is the only one who can answer that question. IMHO

Really? I've sold many chips to this particular bidder. I feel I've sold at a fair price. I know I could have gotten possibly double the price or better (Obviously I would be taking advantage of his lack of knowledge and trust in me)

However, I feel that would be wrong. I assume you don't feel that way. Get all you can, If he doesn't know, it ain't wrong!