[Electric Tire Shredder]

Right. I like @KevB 's idea to DIY a physical inspection, but...

There should be wires going to the seat of every single car made since a couple decades ago, for the occupant sensor. When you find that, if there's only 1 plug with only 2 conductors, there's definitely no seat heat.

 

[Electric Tire Shredder]

I just looked under my own seat & was initially surprised by the complexity of the wiring harness. I traced one cable to the backrest, & at first I thought this might be a way to confirm seat heat. Then I remembered the "active head restraint" which is likely electrical. However, maybe one conduit is for that, & the second one for the back heater. Click to enlarge:

 

[MaryWhitehouse]

March 22 build Icon with heated seats. Driver then passenger seat