Ramp Fees

I landed at Bridgeport airport in Connecticut to pick up a friend and
ended up at Atlantic Aviation Services. I was trying to get on the
other side of the tarmac to where my friends plane was parked but it
was blocked. The FBO guy waved me in to park and with nowhere else to
go I parked. Before I got off the wing of my plane, I was told to pay
ramp fees of $20.
I told him I was going to leave and he insisted that I go inside and
pay or I would get billed via N number. I went in and complained and
they insisted again.

I paid and commented on their policy which left them surprised.

Is this legal to not have the ramp fees posted and demand payment even
though I offered to leave their ramp immediately?

I think that it is entrampment by having the ramp blocked and the ramp
rat guide me to parking.

Dave