To me, it definitely looks suspicious - but take into consideration that in Greece (where I come from) people keep their cars for an average of 6-10 years.
If I bought a used car, I would definitely not want it to have more than 1 previous owners. Of course, the age of the owners and the category of the car play a role too (e.g. sporty cars tend to be abused and then sold..). Buying a car that had one owner, you can always "weigh" them and try to understand how they treated it. Does the car have full service history? I guess if the reason of selling is convincing (e.g. moving) and everything else looks clear, you could go for it..