There are general ways of telling, but nothing full proof. Here are some recommendations:

1. experience and skill - this is extremely important. Look at how long the company's been in this industry. There are companies that may have been in business for 20 years, but just added paint protection film to their business in during the most current few years.
2. References - keep in mind that with references that quality of work may be highly subjective. We have seen very poor clear bra jobs at car events and owners brag about how well the clear bra looks.
3. Look @ the work in person if possible.
4. Most importantly, do not feel bad by asking them about razor cuts. Some would answer that "we use precut clear bras, so we do not need to trim." If you look at the photos above, these were actually precut clear bras as well. Precut or custom, experience is the key.

Hope this helps
3.