good bet is to call the garage the seller claims to use and ask them when it is due and they can also to check if they did it from their records.
My mate was just buying a high milage Audi A6 from a 2nd hand dealer, and before he handed over the cash he went through all the service slips and noticed the words "cam belt change" were added in pen onto a printed service report from the Audi dealer. So he phoned the dealer, they checked and were able to tell him that it was not done, and also the filled him in on all the other service and recall upgrades that it had been through in its life. they also told him they thought it was a good well cared for car.
So the outcome is he was able to knock the seller down for the new cam belts and also had a full heath check discussion with the dealers service manager, so he was still happy to buy the car.
So it may be a very good way for you to learn more about your 4x4 and find some bargining points as well.
AMQ