In Kaer Trolde harbor, a merchant named Johann Bohner is waiting next to a hut (look for the yellow quest icon). Talk to him and he'll let you know that he needs money because his ship was wrecked. If you refuse, the quest ends.

If you accept, Geralt will lend Johann 150 Crowns. Did you trust him and believe his story?

Well, whoops. You've been hustled. When you return to Kaer Trolde, you will see Johann again and learn that he conveniently forgot about the money. You now have two choices:

1. Turn Johann in. This will result in (easy) combat. You can loot his body to get your money back.
2. Trust that he'll eventually repay you, with interest. If you choose this option, you will indeed get your money (plus interest) later when you meet Johann again in Fyresdal village.

Quest over. Money -- or lesson -- earned.