Quarantine is a must do, no questions asked, and it's twice as important coming from a pet store.
There's absolutely no way you can guarantee the snakes in any pet store are mite free and or RI free.
Customers who own snakes come in and in many cases handle the snakes to see if they'd like to buy them.
You can't guarantee those people don't have mites on their snakes at home or worse yet, a bacterial RI.
It should be "standard operating procedure" for any snake you bring into a home that has other snakes or reptiles.