ariel- almost every fish and invert we as hobbyists have in our tanks has been shipped at least once and many have been bagged and sent multiple times. The one exception to this is fish born in our tanks.
Last Sunday I went to the transshipper outside the airport. I picked up 4 large boxes of fish and inverts for a friend. Some came from halfway around the world. Those critters had been bagged and shipped at least 2 or 3 times before they landed. From there the transhipper rebagged them. My friend then quarantines the fish and, when they are ready, sells and ships them.
I breed some rare and pricey plecos. I have shipped boxes of fish worth many $100s of dollars. I have sent out a few hundredof these fish over the years and have lost only one and it was my fault as I injured it when netting and did not realize I had harmed it. Shipping fish, like everything else in this hobby can be done well and it can be done badly. In that order Sunday were 400 Hasbrosus corys. 300 were DOA. One the other hand there were 100s of amano shrimp and close to 1,000 snails and they all came in looking and doing great.
I can also say that over the years 95%+ of newly acquired fish have come to me shipped to my door.
Snails need nothing special except not be allowed to get too warm or cold. They are sent in styrofoam boxes and heat or cold packs are used as needed. Any aquatic critter being shipped should not be fed prior to shipping. The bigger the fish or snail, the longer the preshipping fasting should be done. the reason is it reduces poop in the bag. Also, during shipping it is dark. This helps to calm the fish. In some cases the shipper may add things to the bag water to prevent ammonia build up or to sedate the fish some.
Interesting shipping fact- when shipping shrimp one must put something in the bag such as plant scraps or other inert material onto which the shrimp can grab to anchor themselves. They cannot hold onto the bag itself and if they have nothing on which to anchor they tend to go nuts and bad things result.