I know nothing of dentex but dealers have a bad reputation for detailing and I personally do not like car dealers. I have dealt with many of them and found them all to be shady in some way.
The fact that they charge $500 for a sealant package means that I wouldn't trust them or anyone they are associated with.
I would tell people where you are located and try to get a referall from someone that has had a good experiance.
Your local stealer will be taking a cut of the total cost and the PDR guy will only get part of it. He could be a wholesale Hack who will drill your door jams for easy access. Take it to an independent shop. You will pay the same price and be guaranteed a good job.