Buying "proven" or "breeder size" females.

Hey guys. I have a question about breeding, specifically, buying proven or breeder size females.

First, a little back round. I've been keeping for about 5 years. I have 3 species (BP, Retics, several boas), all in PVC enclosures or tub racks. Never had mites, never had any RI, etc etc (I guess i'm saying this to insinuate i'm not a total noob)

Recently, I got back into BP's. I've been thinking about giving breeding a go. I've done a lot of reading, and a lot of research, but am not necessarily in a hurry.

A guy local to me has a large BP collection and has recently put up a few breeder females for sale. The one in question is a lemon blast. I haven't messaged the guy about it yet so I have no info, but I was wondering what specifically to look for with a proven female. I've heard stories about people selling breeders that can no longer produce, or if they get over-bred, they can lose teeth, etc - Obviously, before anything else, I want to make sure the safety and the wellness of the animal is intact. However, this is one situation I don't know where to start with. Can you over breed a female? And how do I know if this is a bad buy? Shes a lemonblast for 300, if you were wondering.

Thoughts?