When purchasing a used pottery wheel from someone there are several questions you need to ask before you actually buy the equipment:
-How old is the wheel?
-Has it given them any trouble?
-How has the pottery wheel been maintained?
-What type of accessories come with the pottery wheel (bats, leg extensions, counters, etc.)
-What type of guarantee can they give you if the equipment fails upon arrival?
-Will the shipping be insured to safeguard against damage?
-Will the manufacturer's manual (i.e., operating guide) come with the equipment?
You might want to consider looking at sites that sell new potter's wheels to see if they have used equipment. In some cases companies have trade-in programs for potters; they turn in their used potter's wheel and get a credit toward purchasing a new piece of equipment.