I don't pick up rats by their tails. They start to hate you after that. What I do is slowly move my hand and give them an escape root. If they approach my hand then I withdraw it and then eventually pick it up by the chest. I trained my pet rats, though, so I give them the signal and they know I'm going to pick them up and give them a reward. But then I also spoil those rats rotten... they get rice (cooked and uncooked), grapes, jujubes, raisins, leftovers... and I give them baths too. =P (I also potty trained them)
Just saying... picking up by the tail isn't the best option. If you're breeding you can train from a young age and just pick them up by the chest.
This won't get you money-making insurance. I tried to sell some rats and only managed to sell a few. I was left then with about 24 rats... many too big to sell normally. My number has dropped down to 10 and I've quit breeding them. 'Cause they never seem to sell and my snakes never eat them fast enough.