They have lots to sell (11)

'they' is the definition.
Both the answer and definition are plural nouns.
Perhaps there's an association between them I don't understand?

'have lots to sell' is the wordplay.
'have lots' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'sell' becomes 'auctioneer' (auctioneering is a kind of selling).
's' put after 'auctioneer' is 'AUCTIONEERS'.

Can you help me to learn more?