Ask HN: How do you track traffic quality across outbound channels?

What do startups doing extensive outbound marketing (Facebook Ads, Google Display ads, etc) use to track traffic quality and conversions across channels?

We've tried manually tracking UTM codes in our product, but we can't seem to get reliable results from that approach.

Our marketing spend correlates very well with user acquisition, but we have been unable to reconcile our UTM data with our growth. We're not sure whether it's due to behaviour (tech-savvy user sees ad, but Googles to get to the website) or ad/tracking blockers.

What do you guys do or use to solve this problem?