I don't know what the guy used (FWIW they did a good job), but if I look closely I can see the lines and spots left by the stuff. Whatever it is, it looks darker than my black paint O_o

I was able to get it off from the door panels just under the windows, but try as I might I couldn't get the stuff off the trunklid. Anyone have any ideas?

window tinting, from my understanding, only involves the use of a soap/water mix. when I had mine done, he simply cut out the tint to the size of the window, applied the soapy water mix to the window, and then stuck on the tint and evened it out. the tint has its own adhesive, and the soapy water allows him to adjust the tint as necessary before it adheres to the window. mine was also a professional job, done very well. so, it doesn't seem like there should be any unusual liquid except soapy water, unless your guy did something different.

Whatever you can get your hands on. 3M Adhesive Cleaner, Bug and Tar Remover, Toluene, etc.

this may have something to do w/ the spots

water spots or is it spider web looking? I know you said they used P21S. Take a microfiber or terry cloth and rub, or take it back to who did it and there going to have to buff it out.
I've had Klasse do that, but it came out with a little buffing

Don't use that!!!!!!! If you want to remove it use Dawn. That will take the wax off!