“It’s definitely unique at the moment, and it will definitely cause people to take another look at Microsoft,” said Danny Sullivan, editor in chief of an industry publication. “But I don’t think there’s any guarantee that this is a game changer.”

He added that the process to enroll for rebates was “awkward and confusing.”

The software maker has offered similar incentives for people to use its search engine but not on the scale revealed Wednesday. For example, Microsoft offered large companies software and services credits for every employee who used Live Search in the workplace.

But other analysts said the incentive could get consumers to Live Search.

While most search advertisers pay each time a user clicks on their ad, participating merchants will pay Microsoft a fee each time a customer completes a sale through Live Search Cashback. The fee will be a percentage of the retail price, and when the purchase is complete, Microsoft will return the fee to the consumer in the form of a cash rebate, the company said. The rebates to the customer, in effect, come from the advertisers.