Fluent but shallow, it's stocked by lending library (4)
I believe the answer is:
glib
'fluent' is the definition.
(I've seen this in another clue)
'stocked by lending library' is the wordplay.
'stocked by' indicates a hidden word (the answer is contained or stocked by the clue).
'GLIB' can be found hidden inside 'lending library'.
'but shallow it's' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for glib that I've seen before include "freedom of speech?" , "Fluent but insincere" , "Slippery in speech" , "Shallowly articulate" , "Ready with insincere or superficial words" .)