I'm not sure how the algorithm works (or if there's one at all), but while I was filling it out, I had some anxiety about not qualifying. Once I found out I did, I was excited to fill out the form, which I'm sure most people who are in debt and using this tool are. By making this offer seem more exclusive before the form appeared on the landing page, I'd bet that Bills.com increased conversions pretty significantly.
Trulia did something very similar to Bills.com with their landing page. It starts with a simple form asking for "an address" (which sounds less creepy than "your address," although that's what they mean). Below this simple form field is a bright orange button that contrasts well with the hero image behind the form, and emphasizes that the estimate will be personalized to your home.
Significant improvements can be seen through testing different copy text, form layouts, landing page images and background colours. However, not all elements produce the same improvements in conversions, and by looking at the results from different tests, it is possible to identify the elements that consistently tend to produce the greatest increase in conversions.
Open-ended experimentation. This approach is similar to closed-ended experimentation except that more variations will be added for testing and experimentation will not stop when a winner is found. This method is used by large corporation to dynamically improve their conversion rates and improve user experience. Landing page can also be adjusted dynamically as the experiment results change to further enhance user experience.