I can only speak for my local market area, but we seem to have some of the slipperiest bastards on the planet, when it comes to HVAC repair. I refuse to give a recommendation when friends and neighbors ask me who to call when their AC has issues. I had a neighbor with a 15 YO outside unit that needed help. The first two places he called told him, without even looking, that the unit was shot, and they would charge $4-5K for a new one. The third guy actually inspected the thing, found a bad fan and charged him a hundred bucks to replace it. That honest company was bought out by a bigger outfit.
Several years ago I built a new custom home for a very difficult customer. He insisted on using his own, out of town, HVAC contractor, and an obscure brand of equipment. Since then, the only "authorized" local repair contractor has screwed this customer out of over $5K in repairs and rework of the system. The entire mess is heading to court since this contractor initially did a few thousand in rework on the ducting, claiming it was installed incorrectly, then waited a few years and made the same claim again.
I hope it's not a universal issue, but IMHO, I wouldn't do a thing to an HVAC system without three bids and a heck of a lot of due diligence.