A couple of things to keep in mind. First, what is offered is almost always wild-caught imports. And as I understand it, all caecilians are protected from collection and sale in the countries where they exist in the wild. Thus, all of them that come to market in the US got here in violation of the laws in the countries where they came from, usually because they are exported/imported as "rubber eels" and are passed off as fish. They are "legal" to sell in the US once they are here, so this is really a moral issue for you, not a legal one.
Regarding the laws in NH, you should really investigate this yourself. If you cannot find the regulations online, call your state fish and game office and ask about any and all rules relevant to keeping amphibians. You need to know, not just for caecilians, but for any other amphibians you may ever be interested in acquiring. It's important to be familiar with your state laws.
We don't allow commercial links in posts, unless absolutely necessary. So I edited Thomas's post.