Considering the situation, this car should have any and all basic maintenance chores performed including a valve lash inspection.
However, before going too deep into this thing monetarily I would recommend 2 things. One is to check for oil sludge/coking problems and the other is a compression test; each possibly being related to the other. The compression test means the spark plugs come out so replace them at that time.
The easiest way to check for oil sludge/coking is to remove the valve cover (this is where valve lash inspections factor in) and to probe the bottom of the oil pan with a wire loop during an oil change to see if any tar like substance is stuck to the loop.
If there are signs of oil related problems and/or compression problems then I wouldn't get too enamored with the car. The fact the seller was honest enough to tell you they had done nothing to the car may not mean much. That can also be, and often is, a way of saying that they recently discovered an expensive headache and is their way of playing dumb.
If you have a compression test run you should see readings of 180 PSI and above on all cylinders.