It's a rock rake. Pretty simple tool with no parts to routinely service. So the answer seems to be how it's used and the size of tractor it's attached to.
I'd say use some common sense when pulling it and it will last until you don't (use the common sense)!
As far as needing parts or service for a rock rake, if you can't find a hitch pin or a rake tooth on the internet probably ought to buy the biggest you can from a dealer with warranty!
I have a 6' and a 7' and use the 7' behind a 60HP tractor going through a hay field busting up processed hay piles that the cattle deposit there over the winter. Somehow it says in the shape it's suppose to be in.
txnbygod, buy the used one and see if you can tear it up. If you do, buy a bigger, heavier, more expensive one!!