I like bjones' ideas - very helpful!
Also, to agree with MG - Reading the info is necessary. My husband has been looking for an additional guitar amp, and sees dozens of the same type thing. He almost put a snipe in on one until he read buried somewhere in a long body of text that this one didn't work and they didn't know why. Not encouraging, since the seller is a store with a repair shop included!
My tip is to keep a ruler by my computer to help me gauge measurements when they are given.(The one I use is 18" with English and metric units.) Photos can be so deceiving! A good photographer with a good camera can make a dollhouse look like some your whole family could move into! I have bought a lot of jewelry where gem size is often given in mm and/or carats (and there are charts on the web to help figure that out.) People bid things way high, then later leave neg feedback because "the earrings were so much smaller than they looked in the picture". They just went off the picture and never checked actual dimensions given. I have also bought quite a few mineral/crystal/rock specimens and seen the same thing. Same with seashells. Same with collectible glassware. Same with teapots, etc. Gotta make sure you know what you're bidding on!