My experience shows that under the table = better off leaving those boxes at home. Sure, some people will take the time and effort to look, but:
1. They get in the way of people trying to look at the better stuff on the tables and wall
2. The few extra dollars in sales is not worth the back stress lugging those extra boxes
3. People, for the most part, want an easy and pleasant browsing experience. Ordered boxes, prices clearly marked, etc.
Now, if you're blowing out $0.50/$1.00 books up top and you need to restock, then maybe I would reconsider.
YMMV