I'm not a lawyer, but that line of reasoning sounds like something out of a comedy skit.
"Sure, the law regulates sales of alcohol and sales of firearms, but it doesn't say anything about an Alcohol And Firearms Combo Pack™!"
But there are many types of lawyers in this world. Besides the obvious professional divisions -- real estate vs patent law, trial law vs contract law, etc etc -- you have lawyers who advise their clients versus lawyers who assist their clients. The former are the kind you want, who will tell you what to do to keep everything above board; the latter view it as their job to help you do whatever it is you wanted to do, with the thinnest veneer of "obeying" the "law".
It "works" insomuch as you don't come under scrutiny and your lawyer's legal theories are never tested at trial; a lot of the people making use of this sort of lawyer will rarely if ever actually go to trial -- they'll drag things out until their opponents eventually settle.