I'll come clean right off the bat by stating that I work for a company that makes paint protection film, but I will try to keep the information geared towards all brands of ppf.
Film Care - Many of today's paint waxes, bug removers, etc have petroleum distillates like kerosene or naptha in them. While these chemicals work well on paint, they will harm all brands of urethane films. How quickly and how badly depends on the type of film (there is one film line offered by a company that has an AUTOMOTIVE clearcoat that resists the chemicals). Natural waxes like carnuba are safe, but your best option is to use a purpose made sealant, as it tends to "stick" to the urethane's surface better. While ppf looks like paint, the surface is quite different and reacts to chemicals differently.
Marring - This again depends on which brand of film that you use. Some are easily scratched, while others are not. One film on the market actually offers a self-healing clearcoat making swirl marks a non-issue.
Appearance of Film - Most of the film products out today are vastly improved over what was available a few short years ago, however there are still a few lingering brands that have a visible orange peel effect. TBH, about 90% of the appearance factor is based on the abilities of the installer. If in doubt, contact the film manufacturer and ask their opinion for the best person in your region (as well as a direct comparison of their product vs. the competition). While everyone purchasing a company's product may be on their dealer locator, someone putting their name on the line by making a recommendation will ensure that you are getting the best. If you ask to see pictures, make sure you see some that were taaken from inches away, rather than feet. Even a bad install can look good from a few feet away. Better yet, I would ask to see the produict in person. I can tell you that the quality of the install usually coincides with the price, so be wary of the deals that seem too good to be true.
All in all, just make sure you do your homework on what type of film is best for your needs (durability vs price, basic coverage vs. full hood coverage). As much as I hate to say it, many installers will tell you whatever they have is the best, regardless of what is on their shelves. If you havent done your research, you'll be stuck taking their word for it. A good installer should be confident showing you their work on a black vehicle and they should not hesitate to show you some demonstrations about how durable their film is (not just resistance to rocks, but also staining).
