As others have mentioned, there is a lot to like about this one even if it isn't an absolute classic.
One really gets me though is that Vittorio wants out of the deal because he is tired of being extorted. The other members of the "restaurant developers association" don't seem to mind. So much so, when they have the golden opportunity to spill all and tell Columbo how they pay for rave reviews they don't bother. Also, neither of them report why Vittorio may have a major problem with Paul. They are almost party to an obstruction of justice.
I know I always say this about DEATH LENDS A HAND, but Vittorio always makes me wish he'd use counter-blackmail by THREATENING to expose Paul as an extortionist instead of PROMISING to do it. Of course, then maybe there would be no story (unless that alone were enough to scare Paul).