A little trick I used was to put "bitter apple"(found at pet stores for stopping dogs from chewing)on my hands before i pick him up.When they would nip,they'd get the taste of the liquid(doesn't harm them)and learn that when they nip they got a horrible bitter taste in their mouth.After a while they learned not to nip
Most people just give up trying to train them,thats why you see so many in the bargainfinder
Jim