Man-made item contaminated tart, limiting restaurant's turnover (8)
I believe the answer is:
artefact
'man-made item' is the definition.
(I've seen this before)
'contaminated tart limiting restaurant's turnover' is the wordplay.
'contaminated' is an anagram indicator (a corrupted spelling).
'limiting' indicates putting letters inside.
'restaurant' becomes 'cafe' (cafe is a kind of restaurant).
'turnover' is a reversal indicator.
'cafe' in reverse letter order is 'efac'.
'tart' is an anagram of 'artt'.
'artt' placed around 'efac' is 'ARTEFACT'.
(Other definitions for artefact that I've seen before include "Item made by human" , "Article of human workmanship" , "Human-made article" , "A result of craft" , "Man-made object (maybe found in dig)" .)