Wow, I've heard of a lot of petstores doing wrong things for their snakes...but I've never heard of one trying to feed bp's crickets!! Maybe the crix just wandered in there from their lizard displays...but the lack of answers from the clerk would say otherwise. And of course if their displays are bad enough that even crickets can get from one to another...then you can be very likely to have a case of mites as well. I would recommend using white paper-towels as substrate for awhile and keeping an eye out for teeny tiny little crawly bugs. Also watch to see if your snake is soaking a lot in its water bowl...that can also be an indicator of a mite infestation. If you do think you may have mites, there are various threads already established about how to treat for them...or you can start a new one.

What is your set-up like? (And if you've answered this in another thread, please forgive me for asking again!) If you give us an idea of the size/type of enclosure...what you're using for substrate, heating, measuring...what sorts of hides and water bowl you have...we can help you tweak it and make it a perfect home for your new friend!