I agree a small defect can happen but a dent is not a small defect. After 27 years I have received one iPhone that died and 2 computers fail during warranty. A dent I have never seen on any new Apple product nor anyone of the dozens of Mac users I know. That's a control group of about 60 or so users over more than a 20 year period. That is enough to make me suspect the package was opened before it reached the buyer or terribly handled during shipping. Some customs offices around the world are notorious for theft, opening packages and switching other items during inspection but there is little you can do.We have absolutely no idea what Apple's quality control procedures are. My own personal experience, alongside a few years hanging around on these forums, confirms to me that it is very possible for products to get through Apple's quality control with small cosmetic defects.
If you've never received a MacBook, iPad or iPhone with a small scratch or dent on it then I'm happy for you, but don't dismiss the experiences of other people.