I am a service tech. First off. Secondly, to get the courses you either need to pay thousands to a few schools that will train you. I can think of one that was about 12k last I looked. OR, you need to work for a shop and attend DEMA and/or be sponsored to take the classes in another forum. To just show up and take the classes, you need to show DEMA that you have spent thousands as a retailer with proof of invoices from a major manufacturer selling wholesale to your business.
Now, I am just the tech like I said. However, I do know that some manufacturers give parts for life to the original purchaser who registered it within sometimes 30 days of the sale with a receipt to the factory. Those parts for life terminate when you miss a service interval, miss a service inspection, or sell them to another person.
If you buy from some online stores SOME stores, your warranty may not be valid due to grey, or not proper, chain of supply&custody from the factory to you. Long story short. I buy stuff online. I buy all my life support from the brick and mortar guys that I frequent since airfills are not available on line, someone needs to pay for the compressor.
Ahh...yes...costs add up. $30 for labor per stage, $35 parts per stage on the average depending on brand, costs to fix that leaky SPG spool, replace hoses, mouthpiece tears, batteries, orings, etc. Sounds expensive. The lubricant used on the O rings costs about $60 for 2 ounces. That is roughly 10-15 ketchup tear packets worth, and it's not hard to use about a ketchup packet in about 2-3 sets of regulators between all the parts, etc. Some regulators, I know Atomic for one, does it's environmental sealing at each service, taking about half a normal size tube of toothpaste amount of that $30 an ounce goop.....it goes on and on....and the supplies and stuff to do this work ain't cheap. You can't get the tools at Harbor Freight.
Bottom line, buy it local as far as regs is my motto, and service it at the same place if you can always. No need to convince some guy you are the original purchaser and had it done religiously if you are there all the time.....
My .02 only.