I didn't read that much into the website, but you are right, a very huge red flag. My mom is a breeder and there is always an open door to come visit and take a look around the kennels - as should every breeder I believe.
Also, why an adult? If you aren't wanting a puppy, why not adopt? If you visit petfinder.com you find all sorts of yorkies and yorkie mixes that need loving homes (and adoption fees are not $1500!) For $1500, you can get a drop dead gorgeous Yorkie, and like poster said above, a much better representation of the breed.
You might also want to ask if this dog has been used for breeding. A reputable breeder (in my own opinion) doesn't sell their adults when retired from a breeding program, they adopt them to out to loving, forever homes. My mom always leaves the door open down the road if for some reason they can't care for it anymore or have to get rid of it, it can come back and she'll find another good home for it.
__________________ Glory (Yorkie)  India (Biewer)  and Callie (Yorkie)  |