I think it's always a good idea if you have more to sell and feel the backup bids are high enough, you should contact your backup bidders right away. As a bidder, if I have a choice, I prefer to deal with the person who put up the auction in the first place, but will go where I need to to get the chip I want.

Two other thoughts on the matter. When I'm bidding on an item from someone I have had this offer from before, for an item I'd expect him to have more of, I make sure I bid what I think is a reasonable price, but don't sweat not being the high bidder, hoping I'll get a backup offer. It's the reality of selling the common stuff - if you won't sell it, someone else will.

Also, I wonder about the ethics of selling to the high bidder at one price and selling to the person who wouldn't bid as much for a reduced price. Is this fair to the person who really wanted your item and bid fairly for it?