Is there something I am missing here? It appears that the OP and his wife submitted a TRV application with someone's help. That person came to be viewed as "representative". The application was legitimate and truthful in every way, but nothing was said about having a rep. On that thin ground, they were given a 5-year ban. Seems harsh.
But, the OP also said:
What was the agent's fraudulent act? Not declaring themselves as rep? Is that fraud? This whole thing strikes me (but apparently only me) as a bit strange.