Grandparents owned our local barn years ago and later Grandpa's brother had it.  From the stories I've heard, I've always said I wouldn't take a sales barn if it was free.  (I say the same thing about bars).

The problems included bad checks and trying to keep both buyers and sellers happy.  Both sides always thought the owner was working for the other side. 

Finding help is another problem.  Since you only need most of them a day or two a week, you aren't going to have many qualified people interested.

In the last 35 years, 6 sales barns within 60 miles have closed, including the local barn.  Very hard for a small barn, it seems you need 3-4000 head a week, plus special cow/bull sales.  Never hurts to have a weekly sheep/hog sale either.  You have to get maximum use out of your facilities.