I assume most "Best Offers" on auctions are looking for a price above the starting bid, that would force them to consider ending the auction early.
Sort of the opposite of a BIN, with a "Best Offer".
Would somebody consider it bad form? I don't know. I think it's kind of bad form to put "Best Offer", on an auction item to begin with..........but my etiquette, and somebody's else's etiquette, are often two very different things.
Just assume, no matter what you do.............somebody, somewhere is going to consider it "bad form".
That's not political correctness either, in case somebody wants to jump on that bandwagon.........that's just human nature.