Do you mean it's only had 4 services? Should have had 7 by the end of the year.
I hope he means they're offering to do the next 4 services, rather than it's had 4, but that would be a pretty service package if so. If it's had 4 then the previous owner probably took the "every 12 months or X miles" as the longer of the two rather than the shorter, would put me off to be honest. Then again, my car has no service book at present so only the receipts I can find... at least I know it's been serviced.
Thats my thinking - next 4 services is a hell of a deal. It'd include all fluids at least once and spark plugs.