I think it's best to take the approach that anything wet that comes into your tanks is a potential vector for disease and unwanted wildlife. I've certainly had pests ride in on frags that I've purchased from very reputable Canadian companies -- but also had a plan to deal with those things.In canada just avoid ragingreef, their tanks are not clean. They'll sell you a coral with aiptasia, bubble and something alse (parasite wise) and after they'll tell you "ah, we rise the parasites to feed our fish"...
Fragbox, candy corals are ok. Fraggarage once send me the corals with red planaria.