Your snake will start to sit in his/her water bowel, and you will be able to see the little buggers crawling on your snake. You should have a product called Provent-a-Mite. It is sold online and is the only mite spray that actually works. (they sell stuff at pet stores but it is worthless)

On the same train of thought, pet stores usually know nothing about reptiles and should be avoided (there are good reptile stores but the chain stores are crap)