I guess I must be one of the lucky ones..I have bought 2 used motors in the past year, both were "claimed" to have only had 1 to 1 1/2 gallons through them, when I got both motors I did tear them both apart and both showed minimum wear..One was a Hot Mod P5/N Rex and the Other is a Novarossi Plus 21-7BT..both are ballistic..especially the Novarossi, I have 10 gallons through it now and it's stronger now than when i bought it, I have about 6 gallons through the Rex and it's fast..still runs great..But it is a "crap shoot" I rate it about the same as buying a used electric motor..
..I did pay a bit for the Nova ($200)..but I do know the person who I bought it from, The Rex I paid $90 shipped..and it's worth every penny..definitely faster than any GO .21..