Just tell them you want the same tint as Joe Biden's sunglasses cause that's a good look

Biggest thing is don't cheap out, pay the premium for ceramic tint. It's well worth it. The darkness doesn't change how much heat is prevented, only the amount of privacy you want. I did 15% ceramic Llumar film on my truck all the way around with a 5% brow and have been happy. Definitely illegal darkness level but I've never been pulled over for it.

I have XPEL XR Black. 30% on front, 15% on back. It's plenty dark for me as I'm not a drug dealer.

I also have 85% on the windshield (it's not XPEL...I don't know what brand he put on). Lots of folks use 70% on the windshield since it's not really any darker and adds a bit more protection. But 85% is fine by me.

I drive a black car so the tint looks good without being murdered out. The windshield tint helps a great deal. Your car will still be hot in the afternoon summer sun but it cools down much quicker and stays cooler with the A/C on.