Rat biting me!

Question
I am a new rat owner and am a little frustrated with one of my girls biting me. When I first brought her home she chomped me a couple of times, but then seemed to begin a level of trust; unfortunately, I had to take her to have an eye medicated and upon returning home back to the biting. So, I have given her some space and yesterday I extended the back of my hand for her to sniff as she hung her head out of the top cage door; she had to extend her body to reach and I kept at a "safe" distance, but I kept going and she leaned in with her mouth open which I thought might just be a measure of probing. Nope, she deliberately with no defensive quickness laid into my hand as if in slow motion. I was really stunned because it seemed so deliberate. Nevertheless, I am FRUSTRATED with her and the bloody bites that are continuing. I would greatly appreciate some advice as to how I can stem this if I can. I did not really want a pet that I am unable to trust and socialize with; my other girl isn't exactly thrilled with being handled, but at least she seems to be more in tune with what I have read that rats don't typically bite. Hopefully, you can offer some help. Thanks in advance.

Answer
   Unfortunately many rats that are bred for pet stores are not properly socialized and can come with some bad habits.  Even if she may seem tame to you, it's possible that the biting is either out of fear or aggression, or even protecting her cage.  There isn't a lot you can do, I'm afraid, except to keep handling her and hope that she gets better.  Rats that are not properly socialized from birth can be this way and sometimes even develop it later on in life or after an illness or trauma.  I'd like to tell you that she will get better but in my experience a rat who bites out of fear or aggression (not to be confused with play-biting) rarely improves much.  I have one girl now that can't be trusted, and though she is very friendly and not scared of me, if I try to touch her or even one of her cagemates she'll chomp me.  I've been working with her for a few months and she hasn't gotten much better.

 In the future I would recommend getting rats from a local breeder; they will be much more sociable and should never bite.  Well I really hope she does come around on her own!  Good luck!