The problem is there isn't a wide enough variety of rare or in-demand items to make offers that aren't in bulk. There are 4 currently desirable items in game right now. 3 of them (clocks, firewalls, bat magics) aren't necessarily "rare" anymore, at least to the extent that many people have multiples of each. So a person would have to offer them in bulk for someone to be bothered to trade a flip hat, which as far as I know, nobody has extras of (though there may be a couple people out there hiding an extra or two away right now).
Be patient, wait for more releases/events.