Look for high visits with few leads, a conversion rate that stays flat after changes, and a source that only works on one device. When two or three of these show up together, test a cheaper alternative.
1. High visits, few leads
Volume feels good, but visits that never turn into leads are cost, not progress. Compare leads per source, not visits per source.
2. A conversion rate that will not move
If you have changed the offer, the page or the targeting and the rate stays flat, the problem is probably the traffic itself.
3. It only works on one device
A source that converts on mobile but fails on desktop (or the other way around) may be a targeting issue. Split the report by device before you decide.
When two or three signs show up together, run a small test with a cheaper alternative and let the data decide.

