Best balance sheet surveys (6)
I believe the answer is:
plumbs
'surveys' is the definition.
The definition and answer can be both related to thinking as well as being verbs in their -s form.
Maybe they are linked in a way I don't understand?
'best balance sheet' is the wordplay.
'best' becomes 'plum' (informal term for best or top-class).
'balance sheet' becomes 'bs' (this could be a standard abbreviation of which I'm unaware).
'plum'+'bs'='PLUMBS'
Can you help me to learn more?
(Other definitions for plumbs that I've seen before include "Gets to the bottom of" , "Sounds" , "Reaches or experiences, say the depths" .)