Clue: Love fine 8, say, in tiny new case, as one may well believe (2,4,9)
Answer: ON GOOD AUTHORITY
Explanation: Definition: as one may well believe 
**O** ("love") + **GOOD** ("fine") + **AUTHOR** ("8, say" (*see 8 down*)) *in* *(tiny), so **O-N-GOOD AUTHOR-ITY