[Omega] looking for used 3511.50. I'm looking at eBay listings and have some questions.

A simple ebay search for Omega 3511.50 in US only brings up a few choices. In great condition looks like the price range is showing between $1500-1700. What should I be looking out for in listings like this? Over polished? No box or paperwork etc? Seller reputation obviously.

Omega is a quality watch that is in my price range and I like the brand recognition and reputation. I like the 3511.50 over the 3510.50.