Scam involving grandad’s first bill for drink (6)
I believe the answer is:
cognac
'drink' is the definition.
(Cognac is an example)
'scam involving grandad's first bill' is the wordplay.
'scam' becomes 'con' (I've seen this before).
'involving' means one lot of letters goes inside another.
'first' indicates taking the first letters.
'bill' becomes 'ac'.
The first letter of 'grandads' is 'g'.
'con' placed around 'g' is 'cogn'.
'cogn'+'ac'='COGNAC'
'for' is the link.
(Other definitions for cognac that I've seen before include "High-quality brandy" , "Good brandy" , "Type of brandy" , "(French district famed for) fine brandy" , "Liquor" .)