If you're like me and buy a hat, get tired of wearing it and would rather have your big GP stack back, be ready to take a loss. The greedy ass elite merchants with 10-20 hats of each color in their bank have a complete hold on the party hat market and will force you into taking a huge loss. As soon as you go to sell it they will put at least one, often two or three of the same hat color at a sequentially lower price on each one to make it look like the market is saturated, intending to frustrate you into dropping your price way down. Once you go low enough, they swoop in and buy it.
They will then pull all the hats and just put one back up at around the original price you paid for yours.
Just a heads up warning. Only buy a hat if you're planning on keeping it forever. Don't play their greedy ass manipulation game where the rich get richer.