One thing I've noticed so often is Ebay and CL sellers (and elsewhere for that matter) who don't know how to measure or express the size of a bicycle in a generally useful way. You get stand-over with flat tires, downtube length, seattube length with contact points not specified, measurements in inches with unknown rounding up/down/sideways, guesses, "It's about right for someone 5'9," "I'm 5'9" and it's great for everyone I know," as well as top tube length and effective top tube length. It's really a crap shoot unless you ask a good question, actually get an answer, and become convinced that the requested measurements were done right.
You have to be prepared to get something that's wrong, if you can't check it out in person.
Road Fan