When you as the Google Ad Campaign Manager don't have a clear cost per conversion or cost per lead to aim for in the Google Ad Campaign, you're left with the task of trying to drive the cost per conversion down, down, down, as low as possible.

There are 2 problems with this strategy:

1. Driving down the campaign's cost per conversion will eventually have an impact on total conversion volume. In other words, you'll get fewer conversions/leads in a given time period. Where do they go? To your competitors who are willing to pay more per lead. Which brings us to...
2. You can't count on your competition being ignorant when it comes to how valuable leads are to their business, which means that if you just keep trying to lower your campaign's cost per conversion, eventually your competition will just get a larger chunk of the pie because they're willing to pay more per conversion/lead.

Ideally, you'd want to set up offline conversion tracking for lead gen campaigns so you can import offline sales conversion data and optimize your campaign based on return on ad spend (ROAS).

Of course, if your sales cycle takes longer than 90 days then the next best thing is to import qualified lead conversion data, which you can do using software like WhatConverts. Both will allow you to compete more effectively in the Google Ad Auctions & it'll make it easier to maximize conversions and profits.