Are posted speed limits real laws, or just guide lines ?
They are real laws. Based on safety for all drivers at all times based on average traffic on an average day or night in the area.
But, if you're driving 65 in a posted 65 but EVERYONE else is driving 80... you are a risk to safety. You ARE a traffic hazard. You might not get a ticket but road rage comes into play and / or the real possibility of you causing an accident that might kill our maim real people. . And all the BS that comes later in court and your costs. If that is you, stay in the right or slow lane.
On the other hand; If it's 3AM and you're the only dude on the road going 80 in a posted 65 zone. You'll probably get a ticket. You earned it.
The rules are rules... 'real laws', based on safety. The local court in each juristiction deal with this and the judge or judges won't be dismayed.
Cops are there to enforce safety. And, Cops are human and some are understanding..... And some are not.
If pulled over, say "Sir or Ma'am" and show respect to the law person. It goes a LONG WAY to prevent a ticket.
If it's posted on public property it's usually legit.
In a store parking lot, or private property, it's not law but up to the judge... usually. But I've never known a real cop to ticket for private property violations.