Mutual concession from company marks guarantee (10)
I believe the answer is:
compromise
'mutual concession' is the definition.
(two parties making concessions)
'company marks guarantee' is the wordplay.
'company' becomes 'co' (abbreviation).
'marks' becomes 'M' (former German currency).
'guarantee' becomes 'promise' (I've seen this before).
'co'+'m'+'promise'='COMPROMISE'
'from' acts as a link.
(Other definitions for compromise that I've seen before include "Middle course" , "Trade-off" , "Give-and-take" , "accommodation" , "Settlement" .)