Those are different models. Ads can be sold pay per view, pay per click, or even pay per conversion (the store reports when the customer buys something and only pays for that).

These can be converted by multiplying with the estimated probabilities. For example, if the scammer is willing to pay $1 for the click, and the probability that the user will click is estimated to be one-in-500, the view would be worth 0.2 cents.

If the scammer is willing to pay $20 for the conversion (because it means they successfully scammed someone out of $30), they'd need to succeed scamming one in 20 users that clicked for this to work out.

Works the same for legit businesses of course, where the business will consider total lifetime value (not just the current sale - you might also subscribe to something and keep paying for 2 years, or come back to buy again). Advertising / customer acquisition costs are a huge part of many businesses, which is why running online ad platforms is so obscenely profitable.

In this case, I don't know who in the chain will do the conversion - if the bid will be for a click and the ad platform will estimate how likely you are to click, or if the bidder makes the guess and bids based on that. The bidder in this case would be another ad platform of course, acting on behalf of the actual advertiser, and nobody in this "ecosystem" trusts each other. It's full of companies trying to scam each other or companies offering services to validate that the data someone is feeding you is real.