I know a breeder who told me a story about a snake he got from BHB...
He said he bought an adult female cinnamon and he had to run it through the shower to get the mites off. It was like a stream of black coming from the snake as the water and his hand brushed them off. He warned me never to buy from them because their snakes have mites.
I looked over BHB's sale stock at Tinley Park NARBC and I didn't see any mites, though granted I didn't ask to pick any of them up. I only looked at them through the plastic containers.
I've heard the same thing you have, though, so maybe there's some truth to it.