Something similar happened to us on our trip this past winter. It bugged me too...but...
We were sitting on the curb in front of HOP in Liberty Square waiting for Spectro. The CMs came out shortly before the parade and were playing in the street/square with the gathered kids (hula hoops, some ball thing on a string, etc.) and all were having a great time. A CM with a "glowing stuff" cart stations himself across the street (right near the wheelchair viewing area). My son (age 7 with autism) walks a few steps over and starts conversing with the vendor (wow - showing social skills!!!) and walks back to me and says "Look, the man gave me this Stitch." (a glowing, spinning thingie the CM had put into my son's hand) I said "Wow - did you say thank you?" (We had just been YOMD winners the day before - was this more pixie dust?)
My son said "Yes, I did! But I'll do it again!" then he went back over across the street to say "thanks" but returns to me (thing still in his hand) and says "Stitch costs $16 dollars." WHAT?????
I told my son he had to give it back - that he had his own Buzz Lightyear glow spinner (bought at huge clearance prices at the
Disney Store before the trip - thanks dis budget board folks) right here in our bag. (Quick, quick grab it and show him...)
Of course, HUGE meltdown...tears...yelling..."but I want Stitch"... My husband went over with my son for the transfer/return - if I had, I might have gone ballistic! To me, this was over the top. Unfortunately, it is pretty obvious to any adult who spends more than ten seconds with him that my son has a neurological disability, and to put him in this situation did not make us happy. We were kind of able to distract him with the games the other CMs were playing and then the parade started...and that was it.
My guess is that this sales technique "works" more often than it fails - many parents will just fork over the dough, rather than have an unhappy child - especially at WDW. I'm just too much of a meanie/cheapskate!