Here is my take-
I would ask why he wants so much for the dog. I know nothing about dobermans or what one should look for regarding bloodlines or performance or what not, but I would think that for an adult dog to go for that much, it would have to have some type of performance title and come from truly impressive bloodlines.
Also, why does that dude want to get rid of Abby? Just for the money or does she not fit into a breeding program or what's the story morning glory?
Just do your homework. Don't settle for the first pretty face that you see, because that's often deceiving and will end in your regrets.
If the other posters say that dobermans are same-sex aggressive, I'd also not go with a female. I'm sure that if you got into contact with your local doberman breed club that they would steer you in the right direction.
If you're a newbie to a breed, then the breed club is the best way to start. You may even want to go to a few shows and meet some dogs/kennels. IMHO- that's the best way to start on the endevor. That way, you can see the animals up close and in a variety of settings.
In the last sam show I went to, I saw a lady in the ring with some very pretty dogs. I was impressed with them, and I had never heard anything negative about them. However, after meeting her, I decided not to get a dog from her, because I knew she'd be a terrible mentor.
She was not interested in speaking with me, and was quite condescending. If you go online, you'd never know anything like that, and I think that's a pretty big deal.
For that much money, you should go for the whole package- a good kennel, mentor, bloodlines, titles, etc.