At risk of sounding harsh, this is what happens when stupid and/or greedy people watch too many shows on television.
There are two important things that make their expectation unreasonable...
NO legitimate couponer makes 75+% off on any kind of regular basis; on rare occasion, maybe, but not frequently or reliably. (To be clear, I am excluding those who use coupons fraudulently)
Secondly, I get the feeling they're expecting someone to be able to find a way to buy exactly what they'd normally buy, but for less money. The most substantial couponing is when the grocery list is matched against the coupons, not the other other way around. Even then, what one buys with the coupons is rarely with enough breadth to cover the diversity of an average family's eating habits.
The ad was posted by someone looking magically spend just a few dollars to get a substantial savings... the equivalent of getting something for nothing. Bet they haven't hired anyone yet.