When at all possible, go with a
reputable breeder ..not just any breeder (I can tell you horror stories about "breeder rats" ..and "pet store rats", for that matter).
I've raised a two litters here, both accidentally ...and handling the babies is key in their behaviour later on. That being said, time well spent with an older rat from ANY situation can also yield a very well behaved, social rat kid. It really can.
I have rattie kids from pet stores, reptile store's feeder bins, and some from breeders. They all know their names and respond to it.. none of them bite at random or out of fear, etc. ..they all will snuggle with me, but the girls definitely prefer to romp and stomp more
My newest rescue is Koda.. a very large dumbo variegated boy that has not been held or handled very much in his life (or.. he's been terribly mishandled) ...so he and I are working on trust issues with my approaching hand ...and his venturing out of his cage to come to me. He has not bit me once in the entire time I've dealt with him ...but he does drop large, heavy fear poop bombs if I move too suddenly
Your best bet is to find a reputable breeder in your area ..or within rattie train distance... and start communicating with them now. You can also look on petfinder.com and find ratties that need their forever home ..and the rescue where they are being fostered already socializes and assesses any issues that they may have before they are adopted by you. One of my dearest friends operates a rescue in Nebraska and she does wonders with the "babies" that come through her home.
You can check out some of the rattie forums, as well. Goosemoose has a very active rat community ..The Rat Shack does too, I believe.
Good Luck!