lots
Make sure it has a CPL tag unless you want headaches, Inj. pump shouldn't leak, the the cap is off of the aneroid then it may mean they might have messed with the fuel screw (I think). Look for leaks, especially on the injection pump, check fluid levels, Maybe even bring a squirt bottle ( Soapy water) and see if there are any bubbles around the injectors. You do much more with out "wrenching"- like a compression test. If it has an oil gauge you should look for around 30 at idle and around 60 revving.