One seizing stock up in Cairo's sales (5)
I believe the answer is:
lasso
'one seizing stock' is the definition.
(rope for seizing stock - stock can mean cattle)
'up in cairo's sales' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'in' indicates a hidden word.
'ossal' is hidden within 'cairos sales'.
'ossal' written backwards gives 'LASSO'.
(Other definitions for lasso that I've seen before include "Cowboy's noosed rope" , "Rope for throwing" , "Rope with 20" , "something to catch beast liable to run off" , "One may be caught by this" .)