While no one likes being taken advantage of, as someone with exposure to the whims of the general public, you pretty much have to expect that kind of thing from time to time. In a way it is flattery as someone turned to you for guidance. Unfortunately and for whatever reason the person felt the need to use deception. No harm done, really. It’s not so much different than going to a car dealer (or any retailer) and chatting the sales person up.
Until the client signs a contract they can and will do as they please. For some the contract isn’t an impediment to deception, but what a contract gives you that a phone call doesn’t is recourse.
If you feel the need to be vindictive, you have options. Bill’s suggestion is a classic. I know someone who got jerked around and in retaliation they put up flyers all over the jerker’s neighborhood including 2 high schools that the jerker was going to hold a rave at the jerker’s house, starting at 10 PM. I heard that several hundred loaded teenagers showed up throughout the night.
But first, why do you feel the need to be vindictive? All you did was share some information. Sure you were duped, but you’d do the same for anyone who calls and asked, right?
IMO the important thing is that people call you. That means you are doing a lot of things right. I think the expression is: Don’t pet the sweaty things and don’t sweat the petty things....