You can set whatever price you want or start whatever kind of bid war you want. No trade is legally finalized until the items are traded over. You have the right to cancel a trade at any time before items are transferred. It might be "bm" but that doesn't mean you can't do it. I'd say if you set a bin, someone bins it, and others are still offering high, sell to who ever offers the most. You're allowed to do that. You can even set a bin and still not sell to anyone if you change your mind.