These guys are awesome, they're honest. If they come to your house to service your HVAC system they actually "service your system" (shocking). I was a commercial construction executive for almost 20 years and I've seen A LOT of shady stuff.
********If you see an ad for a low cost ($50 or less) service special RUN......RUN AWAY from that company as fast as you can!******
Here's how these guys work......their technicians are on 100% commission, if he doesn't sell you "something" he doesn't get paid. If he doesn't consistently sell customers "something" he gets fired. No company can afford to come to your house for free (do you really think you can trust them?). A company can't even be profitable having a technician drive a van to your house for $49 and be profitable. For $49 they're not "servicing" anything, they're just visually looking for things to sell you (see 100% commission above). So don't fall for that BS!
Go with someone you can trust.....Efficiency Mechanical.