I've found that, as a dealer, you will upset certain buyers no matter what you do. I thought the low 'automatic reject' would solve the problem of having to interact with low-ballers, but found that some of them will do what the OP described, increasing the low-ball offer until they have used up all 3 offers. Then they will contact me and ask for my bottom-line price.
Peter summed it up well when he said that low-ball offers are not negotiating in good faith.
One more point - it's no big deal to get an offer of $15 on an $80 card. But when the same person puts in 5-10 such offers at the same time, it's a pain in the ass.
As a buyer, if you are going to make a low-ball offer and you genuinely are clueless as to the item's value, then just say so. The seller will almost always respect that. I've done it before and never gotten a rude response from the seller. If the item was genuinely priced ridiculously high, my 'clueless' offer is sometimes actually accepted.
This is all about being a human and interacting with other humans. Once you learn how to step over the genuine a-holes, it's not all that difficult.
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$co++ Forre$+
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