Second-rate auction item — dry piece of writing (4)
I believe the answer is:
blot
'dry piece of writing' is the definition.
(I've seen this before)
'second-rate auction item' is the wordplay.
'second-rate' becomes 'b' (second grade after A).
'auction item' becomes 'lot' (a lot is an item for sale at auction).
'b'+'lot'='BLOT'
(Other definitions for blot that I've seen before include "Dark mark/stain" , "stain on reputation" , "Stain left by spilled ink" , "Cross out; inky mess" , "Smudge of ink" .)