The main part is to check the backlink profile, ensure it has some good links that would be hard to make and relevant to the niche you are looking for, and also that it has a relatively clean content history.
If you are looking to sell a domain after registering it, you will want to make sure that the history is very clean, people don't want to pay big bucks on a risky investment. However, if you are looking to use the domain yourself, and it is not at auction, you can snap it up for a negligible cost and give it a shot. I've used many domains recently that have had some dodgy content history and they rank really quickly.