What does this incident reveal about the economy in Maycomb?

Which incident are you talking about? There are a number of economies in the fictional town (and county) in Harper Lee's novel To Kill a Mockingbird. Let us know what incident you mean and you'll get some good answers, I'll bet. This novel is full of material for discussion.

The non-monetary payments from Mr. Cunningham to Atticus Finch tell something about the economy in Maycomb, for example. In the Depression era, money was hard to come by, and in this largely agrarian region in Lee's novel, the farmer pays his lawyer not in cash but in firewood and turnip greens.

Not everyone is poor, of course, and some people still have money to buy luxuries. There's a brief reference to out-of-town travelling salesmen (selling furs) in one place in the novel.