The best way to tell if used tractor equipment is reliable is to inspect the major mechanical components for signs of wear or damage in both a resting and an active state. If the equipment is mobile, the wheels and axles should be tested as well.
Any piece of used tractor equipment runs the risk of having hidden damage or breaking down due to the way it was used by its previous owner. As such, the buyer should inspect it herself to make sure that it is in proper working order. If she doesn't have the proper knowledge of equipment, she needs to have a third party, such as a tractor mechanic, inspect the equipment. Common issues include unexplained knocking or rattling in the engine block, jerking or stuck articulation points, low pressure in hydraulic components and incomplete motion in the power take-off shaft.
In some instances, such as auctions, it is not always possible to physically inspect the tractor equipment. In these scenarios, the buyer needs to look at the machine's maintenance log to find out how often it received servicing and what, if any, repairs were made. If the unit doesn't have a maintenance log or any similar documentation, it is a considerably more risky purchase.