Flattery is the infantry of negotiation

यस्माच्च प्रियमिच्छेत्तु
तस्य ब्रूयात्सदा प्रियम् ।
व्याधो मृगवधं कर्तुम्
गीतं गायति सुस्वरम् ॥

- चाणक्यनीतिः

We should always speak sweet words that please the person from whom we expect a favor. To hunt for a deer, the hunter sings a melodious song first.

Keep your words soft and sweet.
Flattery is the infantry of negotiation.