Dolinski found that people were more likely to mind the woman's grocery cart when they had been previously asked to fulfill an unusual request — to tie someone else's shoelaces.
(Source: NPR, Tie My Shoes, Please: How Persuasion Works)
I remember the door-in-the-face technique being used on residents in the Bay Area a few years back.
"We're going to hike the bridge tolls to $10!" (From $3 or $4.)
"At least it's not $10!"