When asked to put in opening hours, if the sign in the window says 0800 daily, you don't write "well, I was there at 0830 last Wednesday and they weren't open yet, so maybe 0900?". Similarly, you don't write "I parked there for two hours yesterday and I didn't get a ticket"
If there are official-looking signs (not a scrap of plywood with NO PArkiNG written on it with a marker), I don't think it's the cartographer's job to investigate whether the clamping company is legitimately authorised to demand a release fee, how thoroughly the operator enforces restrictions, or how long the warden takes on their rounds.
The OSM community generally holds that access-tagging of a feature should be based on ground-truth; for parking spaces this means defaulting to what is the local law, and specifying exceptions if signs indicate that it is private parking.
