You are absoulety right, you are being ripped off ( cheated out of ) a chance to win a prize / money and get a fair shot.
This applies to probably only Bream and Whiting species.
So, what do you do.
I would contact the organisers of the comp you participated in and inform them of your concerns.
If you feel strongly enough that you have been disadvantaged by the " cheats " ask for your money back, or at least ask that an investigation be done into the suspected cheat and his fish !
I have sent you a pm to explain futher.
Anyone else who feels the same way, should make thier feelings known to the organisers of any comp they enter.
These practices are coming to a head and I feel things are about to change. We need people power to help the process.
Cheers Phill