One of the old tobacco laws that now applies to e-cigs is this:
Do NOT give away free samples of e-cigarettes or other ENDS – Electronic Nicotine Delivery System, including any of their components or parts.
Here are some of the others:
Check photo ID of everyone under age 27 who attempts to purchase e-cigarettes or other ENDS. Only sell e-cigarettes and other ENDS to customers age 18 and older. Do NOT sell e-cigarettes or other ENDS in a vending machine unless in an adult-only facility. Beginning in 2018, do NOT sell or distribute e-cigarettes or other ENDS without a health warning statement on the package. Beginning in 2018, do NOT display advertisements for e-cigarettes or other ENDS without a health warning statement. If you operate a vape shop that mixes or prepares liquid nicotine or nicotine-containing e-liquids, or creates or modifies any type of ENDS, you are considered a tobacco product manufacturer and must comply with all of the legal requirements for tobacco product manufacturers.
For more info on the new law: FDA Tobacco Products Guidance Compliance Page