My OW, AOW and DM instructor runs a scuba repair business, and probably services more regulators as an individual than any other person on the planet (or is in the top 3 otherwise). I've watched him service gear, and have talked to him a lot about it. He also teaches the manufacturer service clinics for several brands of regulators, as well as periodically takes the refresher training for other brands (although he usually gives the instructors tips on how to properly service their regulators). He has a state of the art facility that automatically tests each regulator after servicing for 15 minutes of simulated diving and provides a complete printout back with every regulator.
Some comments from him over the years: It's more cost effective for dive shops to have him service gear than for them to have an in house tech do it. Who would you rather have service your gear - someone who specializes in regulator service and is up on all the manufacturers, or someone who does it along side everything else they do? A lot of manufacturers won't sell service kits to shops without techs not certified by the manufacturer; the trend is probably more in this direction because of liability issues. If you want to be a qualified regulator service tech, Regulator Savvy is the basic required reading, followed by at least a 6 month apprenticeship servicing regulators on a daily basis.
I've seen some of the gear he's gotten in that was supposedly just serviced but not working right, and it's appalling how shoddy a lot of service is. If you're going to service regulators, keep in mind it's life support equipment for someone using it, not just a hobby. A lot of the major scuba shows, including DEMA, offer manufacturer service clinics to participants and will certify you to work on their regulators, but you usually need a basic understanding of regulators and hands-on experience to get any value out of it