Not so bad, I’ll wager (6)
I believe the answer is:
better
'not so bad' is the definition.
'i'll wager' is the wordplay.
I cannot really understand how this works, but
'wager' could be 'bet' ('bet' can be a synonym of 'wager') and 'bet' is present in the answer.
This explanation may well be incorrect...
(Other definitions for better that I've seen before include "More appropriate; gambler" , "On the mend" , "punter" , "Gambler; more effective" , "M ore appropriate" .)