Can you maybe explain the white patch of hair on the puppy’s chest?
A small white patch on a puppy’s chest is actually reasonably common (sometimes it’s just a couple of white hairs), and it doesn’t mean a puppy isn’t purebred. You may also see white on the toes/feet from time to time.
You can learn more about why this happens, and see a selection of other Rottie owners questions (and my answers) about this here… White Patches On Rottweiler Puppies.
Unless you have purchased a puppy with the intention of showing (in which case you shouldn’t accept a pup with any white markings unless it’s only a hair or two and it’s an otherwise outstanding pup) it’s not anything to worry about.
Hope this helps. Best of luck with your pup.