Table d'hote menu they say's favourably established (3,4)
I believe the answer is:
set fair
'favourably established' is the definition.
('set fair' is in good or favourable conditions)
'table d'hote menu they say's' is the wordplay.
'table d'hote' becomes 'set' (I can't justify this - if you can you should believe this answer much more).
'menu' becomes 'fare' (synonyms).
'they say's' shows a homophone (sound like).
'fare' sounds like 'fair'.
'set'+'fair'='SET-FAIR'
(Other definitions for set fair that I've seen before include "settled" , "Likely to remain fine or profitable" , "with bright prospects" , "likely to succeed" , "looking good" .)