oxnsox: Is it really that clear?
Yes it appears thats what may have happened, but I read that the OP pushed the button get $8 displayed. Then inserted the card.
The transaction fee would only be added once you've elected your payment method, so if the OP was aware of the fee and had entered $8 then they'd have every expectation that the $8 figure printed on the ticket was the parking fee and a transaction charges would be added (or not).
What the OP should do is go back to the carpark and confirm how the system actually works, before proceeding. Maybe there is a certain ambiguity in the way the parking companies present this. They may be legally correct in notifying you of the fee and expecting you to add it. Knowing full well it's often missed and there's the odd $40-$65 in it for them. Would that surprise anyone??
But then maybe these companies figure we won't do that because it's human nature to bitch and moan and simply pay the fee rather than challenge their ambiguity
In my experience, that's not how these machines work, usually you put the card in first. But I agree with you, if it went down like you described then you could argue it. My guess however is it goes like this: Insert card, select parking (tap-tap-tap, 0.5 hour = $2.50, 1 hour = $5, 1.5 hours = $7.50, maximum time = $8), press OK, "CC has additional 50c trans fee", press OK, take ticket.