If DTA owned the book, then he's crazy for not selling it to Ian for a reasonable price. However, if he was only the consigner, then I fail to see how he's at fault. If the original owner was unhappy with the price DTA set, then he certainly had ample time to find another consigner or call Ian directly and offer the book at a lower price. I just can't see DTA ruining his reputation for a the 10% consigning fee for the difference between what Ian was offering and what the asking price was (probably around $800).
For instance, if I consigened a vintage book I owned to Metro and basically told them how much I'm willing to sell it for within a given time (let's say six months). However, if Metro takes matters into their own hands and sets the books value at 2X what I was asking for, and the book sat there for months after multiple bids were made higher than my asking price....... I'd the furious. Therefore, I'd take the book back and find another, more reasonable consigner that can get my book sold at a good price and not worry about making an additional $500 in consigning fees. If DTA did do something like this and cost the original owner a lot of money, then that guy would be on these boards screaming his head off.