>Shopping comparison enginse are not all the same. Many commreicial comparison engines rely on businesses to submit a data feed to them and those businesses pay per click if a customre clicks through. A rather old model without a way to pay for conversion instead, but that is how most are. Only those that have a budget can do business on these engines, except Froogle. Froogle is Free.
Google recently bought Dulance which will is a crawler based shopping engine. We will what Google can do with it and how it might integrate with Froogle at a later point. There’s a lot of work other comparison engines have done already. Google has a lot of work ahead of them.