It's one of the reasons I stopped going to them. Once I realized that if I saw an AMA for a specific person, it must have meant that they were just there shilling some new project.
There use to be some AMAs of bored pseudo celebs and they would just show up to take some fan questions and then bounce back to the woodwork... thats the type of shit I like.
I think Promotion = Shilling... just a bit more derogatory term.
Most of the time, subs don't let people pimp their personal shit for monetary gain, no clue why it's more socially acceptable if it's Jennifer Lawrence over some dude who makes cool pottery.