I've heard of a GP who offers a "6-month Smile". No matter how bad your teeth are, they are straight within 6 months (but occlusion very often is not perfect). He performs a ton of these and charges the same as an orthodontist. Patients love it because they don't have to wear braces for years.
I would probably find it hard not taking the cases to completion but it's an option if you want to do a lot of ortho but you are not an orthodontist.