Make sure you get actual proof that the cambelt has been done...
Also listen for banging from the rear diff, especially if you turn it hard lock at low low speed, like on a petrol station forecourt.
Other one is brake hard then accelerate and see if the rear diff goes CLUNK on either of those.
Other than that... check the engine temp when you first get in it... if it's cold, don't be too surprised if it runs like a bag of balls for a few minutes, they're forged motors and take a little while to sort themselves out. If it's warm however the guy has obviously pre-warmed it for you and might be trying to hide some nastiness when it's cold.