I've bought several used canisters and find there are a few points to look at before buying. One is to hear it run. When n impeller or shaft is worn, it can make noise and those items are pretty expensive, so people do try to pass their problem on to you. Hear it run without almost totally silent so that you have to feel the vibration on the can. For the smaller size Eheim, I feel those prices are a bit high for my area but that varies in places.