I’ve had the displeasure of bringing in mites from a new purchase many years ago. It tends to makes you even more vigilant after fighting the little demon-spawn. When I had a large collection (42), in addition to quarantining all new purchases, I also pre-treated my cages with a product similar to Provent-a-mite. I did not pre-treat any of this years’ new additions, but did go over them very carefully at purchase and again at home. It’s also handy to rub a damp paper towel over their skin as you will likely dislodge at least a few and they are easy to spot against a white background. That’s also one reason many keepers put new purchases on paper towels or unprinted newspaper. The mites show up better and these substrates are easier to clean versus natural bedding.
It also helps to know your seller. With the exception of Artemis, who I bought off CL, I’ve done business with the other breeders off and on for years. I know they are diligent in caring for their collections, so I have a bit more confidence that I won’t bring anything home. That said, snakes from them are treated exactly the same for pre-checks and quarantine as for anyone else. It doesn’t hurt to be cautious.