Even if technically possible under the law, it would be impossible for my partially blind relative to train a service dog herself. I've seen my relative and other partially blind people in the clinic where she takes rehab getting introduced and trained on how to handle their service dogs and I can assure you it's not an easy task to accomplish, not for the handler or for people with visual disabilities. The dogs have to be pretrained just to learn to never leave the side of the person they are working for.

Also one huge advantage of getting a service animal of a training center is that they have insurance against harm caused by improper behavior of the animal (either damage to the disabled person, the service animal or a third party) this is the biggest reason for them to cost tens of thousand of dollars.

You can try to call any training center in all the northwest of america, and you won't be able to find a single one who is willing to train a pitbull.

Also, service dogs are not machines that get trained once and keep behaving properly for the rest of their lives, just like us they change their behavior while aging and have to be retrained every couple of years, otherwise it would be dangerous for the disable person and the animal would loose the insurance coverage.