Undesirable trade for jam-maker? (7)
I believe the answer is:
traffic
This clue could be a double definition.
'undesirable trade' is the first definition.
'traffic' can be an answer for 'trade' (I've seen this before). I'm unsure of the 'undesirable' bit.
'jam-maker?' is the second definition.
(traffic can cause traffic jams)
'for' is the link.
Can you help me to learn more?
(Other definitions for traffic that I've seen before include "wheels?" , "Trade (in cars?)" , "Illegally push" , "Vehicles coming and going" , "Sort of light" .)