I have a 2004 TC 30 with just fewer than 500 hours. I love mine and it has given me lots of reliable service.
Since it has nearly 400 hours on it, I suggest you start with the service records. If the owner had the rig serviced at a dealer, follow up with that dealer and (1) confirm the services were performed, and (2) see if they'll share any information regarding abuse or problems with you.
If the owner performed the services himself, ask him exactly what he did, beyond changing the engine oil. The 50, 100, and 200 hour services are fairly basic, but the 300 hour service requires changing the hydraulic fluid and filter as well as the oil in the front axle differential case & final reduction gear case.
> Ask for the owner's manual. Does he have it with the machine, or hidden away somewhere (and clean and pristine)?
> Check the rig for any obvious damage or signs of abuse.
> Look around for his implements and find out what he has been using the machine for most of the time, e.g., mowing (an easy task), ground engaging stuff (works the rig hard), or lots of FEL work (works the tranny hard).
> Check the grease zerks (all of the them) to ensure he's kept everything lubed
> While you are underneath looking at the zerks down there, check out the rubber boots protecting the drive shaft to the front wheel drive.
> Check the air filter to see if he's been keeping it reasonably clear / clean
> Check for oil leaks. A little dampness here and there is OK, by any dripping is a red flag
> Check the wiring and hydraulic lines for signs of any excessive wear, e.g., worn spots
> check the tires for wear and tear. At less than 400 hours, they should be in good to very good condition. i.e., lots of tread still available, and no large missing chunks.
> Start the tractor ... it should start up quickly, w/ a lot of cranking. (Make sure you pre-warm the glow plugs).
> If the rig has a FEL, put the bucket thru its full range of motion. Then rotate the bucket all the way forward (so the forward edge is pointing straight down), then gently press the bucket into the ground. If everything is OK, this should lift the front end of the tractor off the ground a few inches.
> Drive the rig around in all gears and all ranges. Make sure everything works w/o any grinding or jerking.
> Take some tight turns and ensure the power steering works smoothly and w/o any squealing.
> Check the clutch and brakes for wear. They both should feel "tight" and "responsive" a rather subjective call I know.
> If the rig has been in storage for a while, he should have placed a spacer (owner's manual recommends a piece of wood) between the clutch pedal and the step plate to separate the clutch from the flywheel.
> Remove the protective cap from the PTO (was it there?), and operate the PTO at low RPM to ensure it works properly.
> Raise and lower the 3 point and ensure it operates smoothly thru its full range of motion.
> Check the all 3 point connections and linkages for excessive wear and tear. Make sure everything that is supposed to be adjustable, is adjustable and easily turns by hand.
That's all I can think of ... but am sure others will have more recommendations.
Have fun, and let us know how it works out.
. If you do buy the "30" use it safely and well and take a lot of pictures. We like pictures