Do you have a product or service and looking to get sales? Are you buying traffic and trying to figure out the conversion percentage?
First you need to have a real tracking system in place. One that will give you accurate stats on the amount of clicks to sales, or opt-ins.
Without accurate stats you are “marketing in the blind”.
Now that you have data on clicks and conversion the next part is to start split testing different landing page and different headlines. Keep split testing until you get a good conversion percentage.
So the real answer to how many clicks before a sale all depends on you split testing different things to find out how to get the conversions.
Until you do all that then I could never give you an accurate number.
Marketing is all about testing, testing, and retesting until you find the winners.