If the deal is good enough and 7 day return privilege will actually be honored, it is perhaps a worth-while risk to take.
Just remember, you are talking about a camera that is plentiful in used market. If, at any point, you feel uneasy, don't. There are many more of those available.
4 years in an air-conditioned room is nothing to worry about. 4 weeks in a humid basement or a really hot attic can be problematic. You are also dealing with someone who wasn't a direct owner of the piece. So any history you may get of the piece is merely an observation.