I trade on liqui.io all the time. It's one of the few places that carry most of the newer ICO and Ethereum tokens like Golem, Iconomi, Arcade City. I haven't messed with their Wings or Decent IOU tokens but I bought quite a bit during the ICOs. I don't know why people would say that exchange is a scam. I definitely wouldn't leave tokens just sitting there, but I don't do that anyways unless I leave a small buy or sell order.
IOU is dangerous trading because you can't be sure whether the site cheats or not, they can create as much tokens as possible to dump on people and make fake pump like yobit
what you are telling can be true because before the coin gets to exchanges they are trading but i am also not able to understand that when you buy IOU they are telling that you cannot withdraw then how can we sell and how is this trading going on. I am also in thinking that their is something fishy on their site trading and we cannot say until we get some good proof of this fishy trading.