My info might be a bit old but here it is:
I know a guy that has dealt in Bama tickets for a long time (long enough to be recognized as a 'known' scalper) and a few years ago he started buying a "scalper" license every year at the advice of another friend that was a lawyer for 30+ years for the Revenue Department. This guy normally wears his license on a lanyard for customers to see - says it has boosted his business through the years.
However, the average fan that sells an occasional ticket on the quad or at BDS does not have to buy a license - thus it is a crapshoot as to how legit they might be.