Why on earth would anyone risk pissing such a customer off by KNOWINGLY selling him a second?
Ok, I'll retract the troll comment.
Simple answer, to make a sale.
Second simple answer, to get rid of it.
Third simple answer, make profit regardless.
Fourth less simple answer, they have the attitude that they will
generally get away with it.
Certain aspects of business ethics travel along a disappearing curve the larger an organization becomes...
I realize you may just want to be a devil's advocate in order to quash rumors, or possibly, defend Wal Mart; however Pollyannaism is blind folly. No large corporation is as "good" or "well intentioned" as their PR works to make the public to perceive. The desire by some vendors to sell to Wal Mart makes them do things and cut deals that make ethics professors blush. In turn, the demands Wal Mart management places on vendors make ethics professors run to the hills screaming diablo propinquo.
Wal Mart is generally quite good for consumers, but hell on vendors.