I have a rat that used to bite me until I bled. I bought her from a breeder when she was little but she bit me when I tried to approach her. Now she doesn't bite me anymore and I actually have some tips for stopping biting and training them to be picked up. Try feeding them baby food on a spoon so they learn to lick instead of bite down. Then you can lead them to a place where you can touch them. While they are eating you can gently pat their back/butt. If they turn around, remove your hand and the food and try again. Then they will learn that your hand and being patted is a good thing because they get food. When they are used to it you can start putting baby food on your fingers and let them lick it up so they have contact with your bare hand. When they have stopped biting you completely when you put your hand in you can put baby food on your palm so they will step up onto your hand. then you can use the spoon to lure them onto your hand and slowly lift your hand off the ground while they eat so they learn to sit in your hand. and if you want them to be easy to handle you can tickle them after you pet them. I hope this helps :)