even if the bid-ask spread is zero, the fact that someone put a bid at that price implies they value the item more than that at most that exact amount of money,

even if the bid-ask spread is zero, the fact that someone put a bid at that price implies they value the item more than that at most that exact amount of money, and if someone put a ask at that price, that implies they value at least that much money more than that item, so it is STILL a non-zero trade. Note that the bid-ask spread is a LOWER BOUND ESTIMATE on the amount of utility created by a trade, which is almost always nonzero. Of course values are subjective, so you could press the "issue bid" or "issue ask" button and a fraction of a second later have your values shift, and then have the automated system execute trades... But I would say... that's life. Maybe don't click certain buttons if your preference schedule is so flighty? Also, sure, someone could have a (metaphorical) gun to your head when you place the bid, which introduces external factors which could violate the platonic ideal that these trades must create positive value.