Perhaps knaves is about right for these (5)
I believe the answer is:
cards
'perhaps knaves' is the definition.
I can't tell whether this defines the answer.
'about right for these' is the wordplay.
'about' becomes 'ca' (short for circa).
'right' becomes 'r' (common abbreviation).
'for' is a charade indicator (letters next to each other).
'these' becomes 'ds' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ca'+'r'+'ds'='CARDS'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for cards that I've seen before include "Christmas post" , "52 in a pack" , "See 11" , "Get one's -----: it's a P45 nowadays!" , "Combs (wool); pack of --" .)