My sandfish skink buries in the sand 99% of the time, and I forget I have it everytime I walk into the animal room. I feel bad sometimes, because nobody wants it, and it won't die! I've had the darn thing for almost 8 years now? It's really a cool animal (quick moving, and swims through the sand with its smooth scales).
A buddy of mine had bad luck with an eel when he setup a fish tank as well last year. The biggest problem seems to be getting them acclimated to new tank water, as the water at the petstore is definitely funked up with bacteria and it probably had Ich or something else to begin with. The transition probably pushed it over the edge.