People in COVID contract fast lane upset person who usually cashes in unscrupulously (4)

I believe the answer is:

spiv

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'person who usually cashes in unscrupulously' is the definition.
'spiv' can be an answer for 'person' (spiv is a kind of person). I am not certain of the rest of the definition.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for spiv that I've seen before include "Flashy fellow who sells dodgy goods" , "Old black marketeer" , "Disreputable and flashy man" , "Flashy rogue" , "Disreputable dealer" .)

I've seen this clue in The Independent.

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