I don't disagree, but now you need someone more competent than someone's grandmother that doesn't get enough Social security running returns. In which case there low cost business model falls apart.They shouldn't be taking any opened oil back. If the cap seal is broken or tampered with, returns should be denied. I think most Walmarts operate like that these days after being burned too often by scammers.
If you get used oil and take it home - and take it back, Walmart will return your money and eat the cost. I don't refuse to buy from Walmart because thieves steal from Walmart by returning used junk. Your blaming the wrong entity.
I presume eventually wal-mart will catch up with this, but then returning stuff will be much more difficult on everything, and everything will be questioned, and no one will be happy then either.