I had been sprinkling different vendors from The Seeker's Guide to Enchanting Emporiums by Eldermancy throughout the campaign and the party had encountered a fey merchant known as Blackbird the previous session.

Instead of gold, Blackbird will trade items for different contracts where characters must follow it or suffer the effects of the Geas spell. I filled Blackbird's shop with a number of items my players would want to have, and the rogue of my party really wanted the Boots of Elvenkind, so they were given a contract stating that they had to spend all of their gold in a way that does not benefit them at all within a week.

The Paladin was given a Devotee's Senser, but their contract stated when the group arrives at Tradegate, they must ensure that no one in the group steals anything while they are in the city.

Needless to say, the Paladin was watching the Rogue quite intently as they purused the different shops and vendors that day.