I don't like selling things. :c
I never know what to sell them for and one time I sold a super rare item from the St. Patrick's event in 2015 and I ended up selling it for less than 1k because I didn't think it was worth anything.

So whoever bought it got it for a serious steal...

Since then, I've not liked selling things, so instead I prefer to donate them to people who may have missed events or may not have the money to buy a CI.