The drow don't have their city under the human city. The city is a Decanter of Endless Fertilizer, so under it there are farms. But drow farmers are a cut above surface farmers; they've got more slaves, more magic, more hit dice, and more opportunism. This one has noticed that if you let a kobold go after you take its stuff, and you give it some pig-grade mushrooms, it'll come back with more stuff later, sort of like pets that fetch very slowly.

"What've you got?" she asks, when one of her halflings runs up to tell her that there's kobolds again.

Alecka has survived trading with the drow more than twice, because she always stands in the back. She also knows how drow see kobolds.
"Pound'a metal scraps! Bones! Two Bigsacka bones! Also special, richwealthy powerful adventurer bones! Stolen from a golem!"

"Idiot, don't you know that rich powerful adventurers want their bones and might send their friends looking for them? I don't want those. Give me the normal bones and the scraps." She snaps her fingers to send the halfling running for a bag of dried mushrooms.

Alecka did not know this.  But before the halfling comes back- this is where the real trading skill comes in.
"Can make powerful magic item from adventurer bones, you sellthemquick, to lady you hate?"

"You said you stole them from a golem?"

"Stole them from a golem in the river. Big man. Had fancy clothes!"  And jewels, and money, all of which, except for one gold coin, went to other power groups.

(This was something of a whale fall event in kobold society)

"I take it you've already disposed of the clothes. Fine, I'll flip the bones."

"greatdingbusiness!"