You may have heard this term before and not been entirely sure of what it is and why it's so bad. "Double Dipping" refers to when the practitioner doing your wax uses the same waxing stick over and over when doing a Brazilian Wax, thus transferring bacteria from the genitalia into the wax pot- and in turn, to another client.
For obvious reasons, this is unsanitary and dangerous. A trained Esthetician should never be "double dipping" because the chance of spreading STI's between clients is high. Clients come to Estheticians with the expectation that the professional has their safety as a priority, but occasionally I've heard of establishments that specialize in Brazilians "double dipping". It's unfortunate and eventually an outbreak of an STI will be traced back to them - the lawsuit that will follow will definitely not be worth whatever they saved by reusing the same waxing stick!
So if you've been going to an establishment that "double dips" I would bring it up with the shop manager, and then I would stop going there. If they're cutting corners by reusing sticks- you just can't trust that your health is a priority when it comes to anything else either.