Ask a lot of questions, be sure and ask if it has ever been rebuilt. Ask them for the compression. See of they are willing to pull the muffler and send you pics of the piston thru the exhaust port.
I have bought a saw or two off ebay and have had no issues. I prefer buying the saw in person. There was one here on AS in the classifieds off of a very reputable member. i'd rather buy one here off an AS member than blind off ebay. The 361 is a fantastic saw, mine has literally cut hundreds of cords in our firewood business. They have a stellar reputation for dependability and performance.