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Google's economist Hal Varian said position and conversion rate are not correlated.
So being higher ranked in a lead business will help you get the conversions before the searcher tires from filling out forms. Who really wants to fill out a form 7-8 times by the time you go through all the PPC ads. So being at the top of the list SHOULD get you more conversions.
But the ranking doesn't affect ecommerce conversion as much b/c that searcher is concerned with a lot of other factors (price, shipping, delivery time, etc.) and only converts once...
Just to clarify - I am talking about a conversion action which is a 'contact us' type request or a lead - not a purchase (which may be different).