Discovered treasure-chests being put up for sale (5)
I believe the answer is:
offer
'put up for sale' is the definition.
(I've seen this in another clue)
'discovered treasure-chests' is the wordplay.
'discovered' says to take the centre (dis-covered - outer letters removed).
'treasure chests' becomes 'coffers' (I've seen this before).
The middle of 'coffers' is 'OFFER'.
'being' is the link.
(Other definitions for offer that I've seen before include "hand" , "show" , "Come up with" , "Provide (an opportunity)" , "Attempt" .)