This short story by Andrew Plotkin is featured in System's Twilight, a now-free game I strongly recommend you play if you can get an old Mac emulator going.
Listen:
The wooden stall was not large, nor was it cleaner or better-kept than the dozen others in that corner of the market. But where the other stalls had bright paint and ribbons to draw an eye or a purse, this one was bare; its only decoration was a splintery shingle, bearing the words "Anything Bought."
"Just bought? Not sold?" Geret began, laughing, as he stepped inside. He faltered for a moment as he passed the threshold; it was dark inside, dimmer than a place ought to have been, with the May sun shining just beyond the open door. But a voice replied, "Yes; I only buy. I enjoy collecting, I fear. An eccentricity."