Slave man, one found in auction (5)
I believe the answer is:
helot
'slave' is the definition.
(slave in ancient Sparta)
'man one found in auction' is the wordplay.
'man' becomes 'he'.
'one found in auction' becomes 'lot' (I can't justify this - if you can you should give a lot more credence to this answer).
'he'+'lot'='HELOT'
Can you help me to learn more?
(Other definitions for helot that I've seen before include "Spartan slave" , "Greek serf" , "One made to work" , "Serf of ancient Sparta" , "downtrodden?" .)