We've "camped" overnight at WalMart several times on cross country trips. We always check the AllStays app to see if there's camping allowed, then call the Manager to request permission. It's always been granted and we usually have a quiet evening - after purchasing supplies/food at the WalMart. Seems to me it's a win/win for both us & WalMart. But we have been a bit disconcerted to see the signs that say absolutely no overnight parking in some of the places we called and received permission. My guess is 4X4Dodger is correct about the signs being just in case they need to ask someone to leave.