I understand your concerns, but it doesn't mean they sell fakes. The high end brands don't deal with small retailers directly. So it's no wonder that they say their authorized retailers are only their direct accounts like the department stores. There are some ways for small retailers to carry high end brands, but it is not so easy either. A friend of mine owns a small boutique. She tried to carry some high end brands, but it required some strict terms with a distributor. So she gave up at that time.
I bought a bag from them in the past and it was authentic. I paid a service to check its authenticity. I have read too many horror stories on the forum, so I religiously check authenticity when I buy something. I'm comfortable buying from them, but that doesn't mean I blindly believe what I receive from them. I definitely check the authenticity every time I buy. I do the same thing to all other retailers except buying from the brand boutique directly.
I understand that once you get some doubts, everything looks shady. We need to educate ourselves not to end up with the fakes.