Should I buy? '05 987 without service records but only 39k miles?

[kk2002s]

4 POs, whats up with that. Not a deal breaker but a blip on the radar
A PPI with Cam deviation measurements, oil leaking will tell you something about the health, no guarantee of course
A look at the condition of the belt, filters, under the front bumper scrapes, rotors, brake dust on wheels, coolant/expansion tank yellowed, Coolant cap ending in 04, WP replaced will give you a quick id as to whether the PO stayed on top of the basics, preventative component replacement.

Don't get lost in the IMS forest or you will never come out.
Many of the forum members are proof Boxster driving goes on with the original IMSB

[husker boxster]

Don't get too hung up on the # of owners. It is 13 yrs old and 2-seaters are life-style vehicles. Something can change in their life and suddenly the 2-seater doesn't fit. Someone may think they need one and then find out a 2-seater does not fit their needs (2 seats but 3+ people, etc). Or they get engaged, married, or have kids that make a 2-seater impractical. Or it's a weekend toy and suddenly job options change or they need to downsize due to the economy (like the little 'adjustment' in 08). The current owner has medical reasons for selling. There are a myriad of reasons sports cars can have multiple owners. It's not necessarily a red flag, but can make the maintenance history trail harder to traverse.