To incompletely perform bad D.I.Y. would imply deceit (7)
I believe the answer is:
perfidy
'deceit' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for perfidy that I've seen before include "Breach of faith" , "Deceitfulness" , "Betrayal" , "Duplicity" .)