The most common and most likely answer to this crossword clue is the 9 letter word WHEEDLING
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More clues leading to the result WHEEDLING
Buddy explains!

The straight part
We know that "act of flattery" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case act of flattery = wheedling.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WHEEDLING mean?
WHEEDLING verb- To cajole or attempt to persuade by flattery.
- To obtain by flattery, guile, or trickery.
- The act of one who wheedles.
- Coaxing, aiming to persuade.