Buying from on line places is one of the big mistakes too many people do. If your looking for used planes then RC swap meets are a good place to go. Couple weeks ago one of the local clubs had one and we saw a ton of new and used planes and everything else needed. I even bought what I thought was a parts engine I needed to repair one of my good ones. Turned out the parts engine was just taken apart and the repair needed was never finished, just needs new bearings. I will just finish this repair and have another good engine. Still need a part for the one I want to fix though.
The best place to buy a used plane is at the field. You can inspect it and see it fly. If your a known pilot and trusted, sellers will even let you fly the plane, just not take off and land it. You can see what servos are in the plane and hear and see the engine run.
The plane I'm setting up now is a sought after ARF that was discontinued, a very good engine and OK servos. By OK they aren't high end digital servos but they aren't junk, good enough for a 60 size plane like this one. Someone will get a pretty good deal with this one and I will have the cash to build my next plane.