Sell up, but first look for antelopes (8)
I believe the answer is:
gazelles
'for antelopes' is the definition.
(gazelle is a kind of antelope)
'sell up but first' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'but' becomes 'gaze' (I can't justify this - if you can you should believe this answer much more).
'first' means one lot of letters go next to another.
'sell' in reverse letter order is 'lles'.
'lles' put after 'gaze' is 'GAZELLES'.
'look' is the link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for gazelles that I've seen before include "Small swift antelopes" , "Swift and graceful like those in 3 down" , "Swift graceful antelopes" , "Animals" .)