''Rogue Traders'' . They were secretly filmed doing jobs for people(at exhorbitant prices for shoddy work etc.) and then they were confronted at the end of the show.The householders knew what was happening and agreed to let the workmen do the jobs.
This might be the programme
funny story about Donal McIntyre, he was asked by an American, i think?
how to spell his first name, he said, Donald without the D, oh Onald was the reply....