Seafood swindle requires private investigator (6)
I believe the answer is:
Here is my best explanation:
'seafood' is the definition.
'swindle requires private investigator' is the subsidiary indication.
'swindle' becomes 'scam' (scam is a kind of swindle).
'requires' is a charade indicator (letters next to each other).
'private investigator' becomes 'pi' ('PI' can be a synonym of 'private investigator').
(Other definitions for scampi that I've seen before include "Type of seafood", "Breaded prawns", "Dish of crustaceans", "Norway lobsters -- Dublin Bay prawns", "Fried seafood", "Large prawns cooked in batter", "Crumbed prawns", "Prawns, usually fried", "Fish dish, often in rings" and "Large sauteed prawns".)