should I purchase a warrantee from dealer?

Look up their reputation, and for any consumer complaints. Also see if the warranty is actually from them or from a 3rd party. I've seen way to many used car dealers offer 3rd party generic warranties which are about worthless. They (the dealer) can be VERY tricky about how they word 3rd party warranties, and a lot of these 3rd party warranty companies allow a dealer to 'co-brand' the warranty so you think it's coming from them direct. If it's a reputable used/new car Volvo dealer then I think you'll be safe, but read the fine print, as they say.