Customers. Off-the-street customers in a retail environment will get to you in short time. For every wonderful and kind customer we had, there were ten absolutely vile people we had to work with. Wal-Mart has a reputation (as does most of retail) as being run by idiots, but that was hardly the case from my experience. From customers that had unrealistic demands and expectations, to those that were outright rude or had poor hygiene, it made things difficult.
Internally, problems were minimal. Occasionally an odd decision would come down from high above, and we would conform to it in confusion and protest, only to have the decision reversed in short time. A better system of getting worker feedback up management could be used. I would have liked to have seen district managers for our department more often, actually in the thick of things, asking questions.