Waste gambling token, which should have been a good investment (4,4)
I believe the answer is:
blue chip
'investment' is the definition.
(I have seen 'certain investment' mean 'blue chip' so perhaps 'investment' could also mean 'blue chip')
'waste gambling token' is the wordplay.
'waste' becomes 'blue' (blue can mean to squander or waste).
'gambling token' becomes 'chip' (I've seen this in another clue).
'blue'+'chip'='BLUE-CHIP'
'which should have been a good' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for blue chip that I've seen before include "Of shares, fairly reliable as investment - like cerulean piece of potato" , "Highly prestigious" , "Type of shares" , "Excellent" , "good stock" .)