Specimen offered by politician in auction (6)
I believe the answer is:
sample
'specimen' is the definition.
(I've seen this in another clue)
'politician in auction' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'in' is an insertion indicator.
'auction' becomes 'sale' (type of sale).
'mp' inserted within 'sale' is 'SAMPLE'.
'offered by' acts as a link.
(Other definitions for sample that I've seen before include "piece to try" , "Small part used to represent the whole" , "Specimen; sound clip" , "Specimen, try out" , "Experience" .)