Im not being funny or anything, but if you park somweher were you are not allowed to and/or you dont display your time of arrival or appropriate badge/disc, then what reason have you to complain about a parking attendant?
They are only doing this job, just like police are when they arrest someone for the theft of a motor vehicle or pull someone for not indicating etc...
I have had two parking tickets in the last year or so, and both have been entirely my fault due to carelessness (parking and forgetting to display my time of arrival disc in a disced area). I have no greievences with it or the parking attendant that issued the fine as both places were clearly marked and had signposts warning me of it (and I am even more stupid because I park in the same area on a regular basis lol).
Look at it this way, whilst you may have a got £30.00 fine for commiting a crime (which you must have to get the ticket), at least you did not get points for it, which you may well have done had it been a police officer. And you were longer then 27 seconds because you have at least 3 minutes to get back to your car and drive away no matter what.
In my experience, I have always found parking attendants to be quite fair and reasonable. I have been caught parked on the double yellows by Kwik Save and in the Wilko's car park waiting for someone without a parking ticket and both times, I have been politely advised by the parking attendant that i should move as they don't want to have to issue a ticket.
If you do wrong, you must be willing to face the consequences if you are caught doing so.