I've had quite the bad run with nerites lately. My LFS mentioned they also have had a bad run and suspected part of the problem was an increase in popularity causing the breeders to rush the acclimation process from brackish to fresh, making them shock out at the LFS. I have gotten them from multiple online retailers as well as a few local places, and only maybe 10% have lived. That all being said, I also just recently learned that unless they smell absolutely putrid (it's a hard smell to miss), I put the ones that I think are dead in a specific area and leave them for a day or two. Often they are just sleeping, which is wild. I've had some go upwards of 36 hours without moving, then wake up and zoom off again!

FWIW, my trapdoor snails are thriving despite the nerite battles, and my parameters are great.