Car, not posh, a good deal (4)
I believe the answer is:
lots
'a good deal' is the definition.
(I've seen this in another clue)
'car not posh' is the wordplay.
I cannot quite see how this works, but
'car' could be 't' and 't' is found within the answer.
'not' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for lots that I've seen before include "Units sold at auctions - plenty of them" , "Large number or amount" , "Oodles" , "Tons" , "Many found in slot" .)