How to choose a tint level for a customer if they don’t know.

Method 1: First and foremost consider the legal restrictions in your state.  Many people who drive high-end models prefer not to be seen, and darker tints on lower-end models can look a bit ‘tacky’ to many. Also, consider what you have to match the other windows to. Most high-end vehicles, and also many trucks and SUVs have 15-20% on the rear, so you might be better off trying to match that instead of doing something different.