Luckily, my neighbor is getting wily and she had the sense to tell the guy that she needed to check on him -- she called me, and some things she told me about the guy didn't add up, so I looked for a Construction Contractors Board registration, and I found that he was not a registered landscape contractor even though he was going under the name of a landscaping company (which show up under CCB). I also called the Attorney General's Consumer Protection office. More importantly, the guy also shows up in the photo listings of Marion County parole violators.
The take-home lesson: NEVER let anyone start working for you, especially on your roof or inside your house, without checking on them first. (You don't want an unlicensed, uninsured person up on your roof, even if they don't intend to rip you off.)
Also, never do a handshake deal with a door-to-door service provider; make them give you a written contract showing exactly what they are going to do for you and how much it will cost. If a business is so fly-by-night to not even have contract forms, they are obviously too fly-by-night to hire. (Conversely, don't be fooled by slick brochures and spiffy forms -- just because they have a truck with signs and matching shirts and slick materials doesn't mean that they aren't also crooks.)
BOTTOM LINE: Every legitimate service provider -- whether it's a pressure wash of your driveway or removing moss from your roof or washing your windows -- will not object if you say that you want to take their business card and you will call them back if you decide to hire them after you've had a chance to check them out. Anyone who insists that they're only going to be in your neighborhood today, or that their registration is "too new to show up" or that they'll be too busy to come back later is setting you up. Send them packing, and call the Construction Contractors Board and the Attorney General to report them.