I agree with 3Lfarms - with proper maintenance (including greasing) I wouldn't be scared of it. You could always do a compression and blow by check pretty easily. A lot of the other items should have visual or audible indicators of things that aren't quite up to par (if any). That said, it's always nice to know what it was used for too - a tractor pulling a finish mower is taking a lot less abuse than one used to dig out stumps and move them around with the rear wheels off the ground...
Tractors seem to hold their value pretty well. I'd start by pricing out a similar new machine at a local dealer and put some numbers together around things like:
1. Is it still under warranty? If yes, you've got some time to work with the tractor without potentially shelling out any large amount of money assuming the warranty transfers. If no, I'd set aside a couple thousand dollars as a safety net.
2. Maintenance. Hopefully it's all up to date. If not I'd check out the manuals online to find our what 1,000 service looks like. Assuming fluids, filters, etc. at a dealer that's probably $500-1,000.
3. Consider what some of the new options are worth to you - remote raise/lower 3 point linkage, 3rd rear remote, etc. that you would find on the new XR41XX series tractors.
Does the current owner have a price they're looking to get?