Pressure testing is used to check for leaks in the cooling system and to test the radiator cap. Sometimes people try to cover up leaks with additives that "seal" the leak. Pressure testing can identify leaking water pumps, hoses, head gaskets, radiators and any other components carrying coolant. Again, any vehicle can be subject to shady sellers attempting to mask a major issue and with all of the additives you can get from parts stores makes it easy to do.
