The most common solution I can find online is to use a PP solution, but it can be dangerous to fish, so you may have to place the moss in a different tank while it "clears up". You may also want to try a peroxide solution. I've been told that you can use that 50/50 with water in a separate tank with NO FISH, and it won't hurt the plant, but you may want to double check.
Bleach dip works to kill snail eggs yes, but it'll also affect your plant's life, hardy plants can only withstand the bleach dip and non-hardy plants will mostly die along with the snail eggs.
I've heard people just leaving it in a bucket with untreated tap water and letting it sit there for several weeks, but I'm not sure if that's just to QT the plants or if it'll actually kill the snail eggs themselves.
I would not suggest bleach dipping with mosses, they're pretty frail as plants and they take so long to regrow.
Ok I tried the tap water method with a previous shipment the plants started rotting. I won't do bleach. I do have PP I am reluctant to mix it for 3 small pieces of moss. I need to find a sterile plant supplier. I've not been happy with what I've recieved.
jadaBlu - I feel your pain! I was concerned with snail eggs with some Java Moss I bought recently..then I found out it was infested with Scuds, ugh. I did a Hydrogen Peroxide dip to kill the Scuds, but I read it probably wont kill snail eggs. Among my research I heard about an Alum dip. You can find it in the grocery store, usually with the spices. You may want to look into that and see if it's something you'd like to try.
Best of luck! I know it's frustrating to finally get what you're looking for, only to find it infested with hitchhikers you don't care for.