1. Is the installer “Bulk” or “Plot”? If you're looking for an installer, you'll want to ask how it cuts the PPF there. You want to find an installer that will use a plotter to cut the film. That's why. If you're doing what's called a "bulk", you'll need to take a large square piece of film, attach it to the car, and use a knife to trim off all the excess, along with the extended edges. I've wrapped various edges in it. For example, on the door, I wrapped all four edges.
2. How often do you use PPF? Paint protection film is a very delicate craft that requires hours of work and effort. If a business only does it 2-3 times a month, that's a red flag and I'd stay away from them and find someone more experienced.
3. Is the shop clean? There's only one way to find out, and that's by going straight to the shop. Ask an installer if they can come over and inspect the area to see how well it is maintained. The quality of a PPF installation depends largely on the environment in which the PPF is installed. If the sthop is dirty, your film is probably dirty too.
4. Do you Wrap Edges? Make sure to find a store that does wraps edges. I went the extra mile and wrapped every edge I could. There are always limits, but I always push the limits to get the best install possible. Some shops won't wrapping, not only will it make your vehicle look bad, but your edging will still be affected by stone chips.
Here are pictures of a non wrapped edge below and bad installation: