I think the problem with this approach is that it only validates the product if you get customers. The average case probably goes like: spend xxxx on adwords, g

I think the problem with this approach is that it only validates the product if you get customers. The average case probably goes like: spend xxxx on adwords, get 0-1 sales. At this point you don't know if your sales pitch is wrong, your product is wrong, you didn't reach the right customers, if the problem doesn't exist, etc etc.