Turn away 10% of customers just at the moment they want to pay you, in order to boost conversion rate of the remaining 90% by 1%. This makes no sense.

My opinion is, stick with:

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I was on Hipmunk last week trying to book a hotel room, and I couldn't buy because the drop-down to select expiration date was overly engineered to the point it no longer triggered the spinner UI. Powered by Expedia! (iPhone 5 running iOS 6.1.2)