Skin beggars

Why are there people who keep bothering others asking to trade skins. When I question them since I like to get new skins they always delay and say they don't want to do it because "I don't trust you etc." and always try to make me give it to them first. Suspicious right? Nor to mention they're are the one's who ask first so it would sorta make sense for them to put in the effort. Really need riot to build a 2 way trade mode. Like Warframe, but for mystery boxes. I think it would make people who do this kind of ask but don't return behavior stop quickly.