There is a problem with the description of the tractor. There is no such thing as a TC350. Is it perhaps a TC35D? If so, $13,500 is a fair price if the tractor is in good condition. If it is a TC35 (gear tractor) then it may be a little overpriced at 1,800 hours. I'd offer $12,500.
I'd first look under the hood at the battery and radiator are for acid leaks and corrosion. You can also normally tell if the loader has been abused by how badly the bucket has been beat up/bent. Check the tractor for leaks and obvious missing/malfunctioning parts. For $13,500, I'd expect it to be in top mechanical condition.