Consumerist has the latest example in a long string of companies bribing customers for good survey scores. A Pizza Hut franchise taped a note to a pizza box offering customers a $1 discount if they bring in proof that they took the survey, and noting that "Only 5's count."
[To be fair to the Pizza Hut--it's not clear that customers would only get the discount for giving the restaurant perfect scores. But the flier could certainly be interpreted that way, and I'm sure many customers did.]
This kind of thing will continue to happen as long as companies keep setting up incentives to improve survey scores without also having strong controls on the survey process. There are a zillion ways to manipulate customer surveys, from blatant (telling customers that "only 5's count") to subtle (selectively reminding the happy customers to take the survey).
Paying employees to deliver better survey scores is almost always going to give better surveys scores--but it won't necessarily give happier customers.