I have used AC Wholesalers, an online website, to purchase a package unit heat pump here in Texas (the existing furnace and A/C were both shot). I delivered it to my handyman, who is also a Journeyman Electrician, and had him build the better pad and set it. Before turning it on I had a licensed A/C technician come out and do an inspection and test it. Total all in for my last 3.5 ton unit was $3,000. This is in a small town where much of the labor pool are generalists so they can keep busy. I had quotes from 3 A/C shops to do the whole job for $4,500 to $6,000, and said no thanks - they just mark up the equipment and labor way beyond what's really needed..
I forgot to mention - I tried to buy one of these units directly from the manufacturers at their re-seller's location in town and they would only sell to licensed AC technicians who are certified with the state. After asking "why?" it was store policy, and not due to any legal restriction. My personal view is that it's unnecessary collusion - just like how many states that require beer distributers. Just a middleman that adds zero value.