Dubious fines collected by city on a regular basis (4)
I believe the answer is:
iffy
'dubious' is the definition.
(thesaurus)
'fines collected by city on a regular basis' is the wordplay.
'fines' becomes 'ff' (I can't justify this - if you can you should give a lot more credence to this answer).
'collected by' indicates putting letters inside.
'on a regular basis' means one should take alternating letters.
The alternating letters of 'city' are 'iy'.
'ff' placed within 'iy' is 'IFFY'.
Can you help me to learn more?
(Other definitions for iffy that I've seen before include "Unsure" , "Questionable (inf)" , "Doubtful, not definite" , "Informally dubious, not definite" , "Not to be trusted" .)