I cut down a few dead trees and branches on my property and didn't really want to pay a service to come turn them into mulch. A month or so later I saw a city truck taking down a tree across the street with a chipper attached that mobsters would be jealous of.

I asked them that, even though my trees weren't obstructing roads or what not, could I pay them under the table to maybe just swing by with that big chipper? "Is anything thicker than 18 inches in diameter?" "Oh. No. Not even close."

They stopped by after the job and explained that they can't take tips and they were happy to help out a resident. "Okay, well how many are in your crew? 4? I'm going to leave this envelope of 4 20s right here, and whatever happens to it happens to it." (Still cheaper than paying a service to come out and they were happy.)