Posters framing quiet people splashing cash? (8)
I believe the answer is:
spenders
'people splashing cash?' is the definition.
(people spending money)
'posters framing quiet' is the wordplay.
'posters' becomes 'senders' (people sending things in the post).
'framing' indicates putting letters inside (inserted letters are framed by the outside letters).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'senders' placed around 'p' is 'SPENDERS'.
(Other definitions for spenders that I've seen before include "Shoppers" , "Big ones buy a lot" , "Purchasers" .)