Crazy promise over time leads to fraud (8)
I believe the answer is:
imposter
'fraud' is the definition.
('imposter' can be a synonym of 'fraud')
'crazy promise over time leads' is the wordplay.
'crazy' is an anagram indicator.
'over' is an insertion indicator.
'leads' says to take the initial letters.
The first letter of 'time' is 't'.
'promise' with letters rearranged gives 'imposer'.
'imposer' placed around 't' is 'IMPOSTER'.
'to' acts as a link.
(Other definitions for imposter that I've seen before include "One assuming a false identity" , "One pretends to be someone else" , "con man" , "Pretender, fake" , "Cheat" .)