Type of business invested in currency - they don't say no (6)
I believe the answer is:
yesmen
'they don't say no' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'type of business invested in currency' is the wordplay.
'type of business' becomes 'sme' (I can't justify this - if you can you should give a lot more credence to this answer).
'invested in' is an insertion indicator.
'currency' becomes 'yen' (Japanese currency).
'sme' placed within 'yen' is 'YESMEN'.
Can you help me to learn more?
(Other definitions for yesmen that I've seen before include "Followers who appear for" , "Crawlers" , "Sycophants" , "They always agree with bosses" , "they obey" .)