Without knowing anything more, those hours are not many.
Generally, a compact tractor's engine will get at least 5,000 hours before needing major surgery. Of course, that is a generalization.
Break in is usually around 50 hours, and 300 is nothing. Valve lash would need to be checked, probably around 400 hours or so, but the owner manual should tell what you would need in maintenance.
You have no way of knowing how the tractor was maintained, and rental equipment can be used by a huge variety of experienced and non-experienced persons. You need to check for bushing wear in attachments, for evidence that grease has been used generously and that important elements are not bent or broken. Does everything work as it should? Are there any leaks when operating the 3pt. hitch or other hydraulic equipment? Does the machine LOOK like it fits the number of hours? A worn looking machine with only a few hundred hours may not reflect the true hours. On the other hand, a repainted tractor would be misleading as well.
I would say that generally, a tractor with the hours your state would be a good buy if it is reasonably priced compared to a new one with the same equipment. Often, a new tractor, with full factory warranty and 0% or low % financing may be the better option. If you can't save a few thousand, at least, over a new one, then I would go new.
John