I have the strong suspicion wfo9 does not like dealerships.
I have some observations here:
1) Even though the sales guy was being "nice" in telling you that you could save money by going directly to the installer, you really cut your options by not having them installed through the dealership. If its done as part of the purchase as a dealer authorized installation you have the force of God behind you if it fails. Without that, you don't.
2) People need to understand that some people (and I don't mean you in this case) do really stupid crap to their vehicles. I am sure you have heard the motto "A little knowledge is a dangerous thing"? Dealers face this all the time.
I will give you an example:
My son (who I love very much) decided to install an amp in his girlfriends fairly new car a few years ago. He didn't engage me because he figured "piece of cake".
After he was done her check engine light would come on, her heat & A/C wouldn't work and her brake lights stopped working. They got me involved out of desperation and what did I discover? He used a screwdriver to poke a hole in the wiring harness grommet on the firewall to run the power feed and cut two wires. One was broke but sporadically touching, the other was about 1/8" apart.
Rookie mistake. Careless mistake. Dumb mistake.
But this is the kind of crap dealerships deal with. Somebody does something crazy, plays dumb and takes it into the dealership and says "It's broke, fix it".
And yes, it was a pain in the rear for me to repair. Not a lot of wiggle room on a wiring harness at the firewall.
3) I live in Colorado and had seat warmers once in a BMW I owned and never even used them. You must REALLY like a warm butt to lay that kind of cash out for something as simple as seat warmers.
4) I just bought a 2015 Trail, it does not have butt warmers. It will not have butt warmers.
I wish you success on resolving this. Ultimately though since you had the warmers installed outside of Toyota, you should be happy they are giving you any traction at all.