To oblige persons often costs little and helps much.

[Cuesta a veces muy poco el obligar, y vale mucho.]

Baltasar Gracián y Morales (1601-1658) Spanish Jesuit priest, writer, philosopher

The Art of Worldly Wisdom [Oráculo Manual y Arte de Prudencia], § 226 (1647) [tr. Jacobs (1892)]
    (Source)

(Source (Spanish)). Alternate translations:

Sometime the care of engaging costs but very little, and is worth a great deal.
[Flesher ed. (1685)]

To be obliging usually costs but little; yet it is worth much.
[tr. Fischer (1937)]

Pleasing others costs little and is worth much.
[tr. Maurer (1992)]