Gold cot in jumble sale (7)
I believe the answer is:
auction
'sale' is the definition.
(public sale)
'gold cot in jumble' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'jumble' indicates an anagram.
'cot'+'in'='cotin'
'cotin' anagrammed gives 'ction'.
'au'+'ction'='AUCTION'
(Other definitions for auction that I've seen before include "Public bidding sale" , "Offer to bidders" , "Competitive sale" , "Public sale by bid" , "Public sale with lots" .)