I've stayed at numerous Wal-Marts, Cracker Barrels, casinos, etc. Unless RVs are already parked there, I usually ask for permission. Once when I stopped at a Wal-Mart in Roswell, NM the young lady at the customer service desk raised her eyebrow, looked at me with her head cocked back and said it was OK to park as long as they didn't get any complaints about me. Complaints? Yeah, like wild parties and stuff. Jeez. Nothing like getting scolded before I'd even done anything. I said I'm 60 and traveling alone, do I look like I'll be throwing wild parties? She said you wouldn't believe what some RVers do out there.
I'm sure that sort of thing happens occasionally, but I've seldom seen RVers misbehaving. Most of us just want to get a quiet night's sleep. The partiers are an example of a few bad players spoiling the game for the rest of us, which unfortunately leads some cities and businesses and citizens to want to ban all Rvers.
Seems the determining factor is usually a city ordinance prohibiting it. A security guard at a casino in Las Vegas recently told me a Nevada state law states that any vehicle being slept in overnight has to be hooked up. A state law? Really? Maybe a local ordinance, not sure, but it was tough to get permission at most of the places where I asked. A manager at a Sam's Club said in her stern and forceful voice, "Absolutely not!"
I prefer to ask for permission at most places instead of taking the chance at a knock on the door later.