That's not quite what this is.

The 'best price guarantee' guarantees the customer will receive the lowest price for their ticket. Google will refund them if anyone gets a lower price.

The airline can release, for 30 seconds only, a much lower price. Then Google has to refund all their customers, and the airline might only sell a handful of tickets at the lower price.

Remember airline tickets aren't fungible. They have names attached, and can't be resold, so nobody can buy up thousands of tickets in a price dip and resell.