A mix-up at the sale (6)
I believe the answer is:
jumble
'sale' is the definition.
(jumble sale is a kind of sale)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for jumble that I've seen before include "Muddle" , "Discarded assortment (for sale?)" , "Hodgepodge" , "Mix confusedly" , "Mixed-up collection (for sale)" .)