Burden with auction involving hollow dud (6)
I believe the answer is:
saddle
'burden' is the definition.
('saddle' can be a synonym of 'burden')
'auction involving hollow dud' is the wordplay.
'auction' becomes 'sale' (I've seen this before).
'involving' indicates putting letters inside.
'hollow' means to remove the middle letters.
'dud' with its middle taken out is 'dd'.
'sale' going around 'dd' is 'SADDLE'.
'with' acts as a link.
(Other definitions for saddle that I've seen before include "Equestrian equipment" , "Seat for a rider, horse or bicycle" , "Impose a task on -- assign responsibility for" , "Burden; seat" , "Cycle seat" .)