IME, turbos can be touchy, esp. if you keep tank on the warmer side (many come from cooler waters off Mexico). However, if you get "good" specimens, they get huge (we're talking golf ball size easily) and will live a super long time. There is a Turbo from the Caribbean that is smaller and has a pretty orange shell that does much better if you can find them, but they're kinda rare.
What you need to do is pick the snails up and give them a sniff...you'll know if they're dead really quick. Also, their operculum will typically fall off when they kick it.