A good way to do this is to examine the metal foot
pedals, which are likely to have originally had a tread, grid or some sort
of design that will now be showing wear. If these are inconclusive
then a more important criteria would be the overall condition of the
machine. Oil leaks and lots of play in the steering and pedal travel
are not good signs.
Of course you also need to remember that quite possibly
someone has gone to some trouble to make the tractor appear newer than it
is with a paint job. That in itself is no bad thing since it amounts
to protecting your soon-to-be investment, but if the tractor you're
looking at has shiny new paint, you should try to imagine
what it looked like before. Also, while professionals will tell you
that a re-paint can actually be harder and more durable than the original,
don't count on it. That shine may be chipping or peeling within a
year, so while a new paint job has its benefits, once it's been applied,
it's hard to tell how long it will last..
When you're buying a pretty low-priced tractor, don't
forget that
replacing a set of tires may cost you $400 to $800, so look at the tires
carefully. Just because they have a lot of tread doesn't mean
that they'll last a long time if they are severely weather-cracked, or if
they have deep cuts. In fact, it's not a bad idea to assume that
you'll be wanting a new set of tires early on and bear that in mind when
setting your budget.
Next, you want to start up the engine. I'm
assuming that you wouldn't be reading this if you were an expert at engine
diagnosis, and I'm not one either, but I can tell you some basic
things to watch for that don't take a lot of knowledge.

First of all, does it start right up? If not,
it's only going to be worse once you get it home, especially after the
weather turns colder. An engine can be in pretty poor condition and
still start easily in warm weather, likewise, just because it doesn't
start easily doesn't mean that it's worn out, but if you have any reason
to believe the seller is has more mechanical capabilities than yourself,
hard starting should be viewed with suspicion. There are always lots
of tractors on the market. For our purposes here, if getting the
engine started in the first place requires any special skills or
procedures, just move on to the next one.