Reportedly auction unmarked aircraft (9)
I believe the answer is:
sailplane
'aircraft' is the definition.
(sailplane is a kind of aircraft)
'reportedly auction unmarked' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'auction' becomes 'sale' (I've seen this before).
'unmarked' becomes 'plane' (I can't justify this - if you can you should believe this answer much more).
'sale' sounds like 'sail'.
'sail'+'plane'='SAILPLANE'
(Other definitions for sailplane that I've seen before include "Glider" , "Aircraft" .)