The wheels indicate that at least one of the wheels was changed. The seat, tires and handlebar don't look stock either - without more pictures its hard to say. How old is the bike? What model? Was it crashed? If it has a carbon fork, and was crashed, you may want to check the fork closely. (Not saying it was crashed - but hard to think of a reason why only one wheel was changed/upgraded).
PS: there is no Sirrus 4 - there is the base Sirrus, Sirrus Sport, Sirrus Elite etc.
Frankly, the price looks good. But a few things that I'm not able to understand:
1. The Sirrus is a flat bar bike - but the bars in the picture look to be riser bars. Non-stock?
2. Tires are definitely not stock, but that isn't necessarily a bad thing
3. Mismatched wheels
I don't think I can comment much more on the price based on that one photo - for all I know, Specialized may have had a model that had all the things I spotted (except the mismatched wheels - am pretty sure that wouldn't happen). I'm not much of an expert anyway - do you have a knowledgeable friend who can accompany you when you go to check out the bike?
I don't think the fork is OEM either, as I *think* I see disc tabs. Not too many frames/forks come with the mounting points for rim and disc brakes- it's typically one or the other (Trek 8.1 DS does come configured as such though).
I think only the frame is original, the rest is enigmatic. I don't mind that actually, was just wondering whether it's worth the buck and whether it's a stolen bike - I had a lot of bikes stolen so I really hate for others to feel that way.