The befuddled geezer, the diaper wearing octogenarian — these are great marks. Myopically peering through laser-concentrating spectacles, they never can see the fine print. Heck, you can get them to pretty much get granny to sign her entire life away, just by making soothing noises in response to her pigeon-like cooing about her monthly budget and maybe flashing her a flirtatious smile.
