Alorael - Oh, I know there is no Quest Log. I really miss it. Handwritten notes are more work.
The Mayor is indeed the auctioneer. He never offered a quest for the wandering ghouls.
I ended up running into those ghouls and killed them. Suddenly I had a dialogue option with the Mayor "Hey, I killed some ghouls. Do you pay for that?" And I was told "No, we're poor." I got a similar message with the barkeep, and his response was "We don't reward for that, but we think the undead come from the north."
So either I missed the quest prompt the first time (and I talked to everyone twice...) or the hint book is wrong.
Thanks for the replies. I'll just keep making Avernum a (somewhat) safer place for all.