Peppermint Shrimp - Lysmata wurdemanni -are often sought after because they tend to eat small aiptasia in the reef. While most LFS will carry these, some are possibly mistakenly sold as Peppermints when in fact they are Camelback shrimp. Camelbacks have a hump that is quite distinct when the animal is viewed from the side rather than from above (as pictured here). They do not harm most corals and fish tend to ignore them. They are usually only visible late at night with a flashlight, as they hide in the rockwork all day long.
If you have slow feeding LPS corals like Fungias, Lobos and Welsophyllia, these opportunistic shrimp may steal food from the coral, literally reaching into the mouth and taking it. You may need to use a dome to keep Peppermints at bay for a few hours so the coral can ingest its meal fully.