I can't imagine being anything other than angry after filling out a payment form and then being told that there was no reason to have done that. On a new web application?
Although I consider the practice unethical, the other side would (does) argue: "Who cares? You are trying to get 20,000 customers and you pissed off 100 to get there."
You wouldn't really have any customers if you weren't accepting payments though, it would be more like you pissed off all of your potential customers just for a bit of market data.
