I am not a lawyer, but I would imagine you'd be legally covered if you required all customers to sign a statement that they understand that transporting a burmese across state lines is a federal felony under the Lacey act and that they don't intend to commit that crime with the snake they're buying from you. If, when questioned, you produce that signed statement, it should be pretty good evidence that you're not party to a crime. Kinda like how gun shops have to keep records of every firearm sale proving that they did the required background checks and followed all regulations, etc.