Like the others have suggested, WalMart is run by arrogant pricks. They treat vendors like crap, almost as though asking for floor space for a display is stealing from them. Some of the older, long-time members of management actually have a little card in the collection of cards under their name tags that says "Just say NO to vendors." I had to approach a grocery manager (guy named Bob who had 20-30 years with WM) about a display one time and he showed it to me. Didn't say a word, just flashed the card. Pricks. Hardly surprising when their company logo looks like a big yellow a--hole.
Lack of communication is also a big problem. On the rare occasions that a display is ok'd, we will set it up and on our next trip into the store, it will be in the backroom, replaced by some other display given the ok by a different member of management. And then they b--ch about too much backstock.
One of the bread guys and I used to joke that if either of us ever heard that there was a massive fire in the store we serviced, we were each others' alibi.