I think that perhaps a more descriptive terminiology might be in order here.

Instead of using terms like "client" and "competitor" relationships ... I prefer "Buyer" and "Seller".

I don't think that advising people not to bid on an item because one knows one party or the other makes much sense. It's a free market place. Bid against anyone ... Sell to anyone. Highest bidder wins.

I've purchased items on ebay to re-sell at higher prices to my chip customers ... some of whom are not on-line. That's why in my opinion ebay sales are not the final barometer on worth. No one knows for sure whether an item has been purchased for re-sale or put into one's collection ... to be sold at a later date.