Target CPA is an average, not a ceiling
People set a target CPA believing it caps what Google will pay for a lead. It does not. It sets an average Google must hit across the campaign, and the algorithm is free to hit it any way it can.
That means it will happily pay £30 for a click it thinks is a good lead, provided it can buy enough £3 clicks that also register as conversions to bring the average back to target. When every form, call and chat counts as one conversion, cheap junk qualifies. Wrong numbers, existing customers ringing about a job, people trying to complain to a national brand: if the call lasts thirty seconds, it counts.
The junk funds the good leads. The more competitive the auction gets, the more junk has to be bought per good lead to hold the average, which is why an account on a fixed target gets worse as CPCs rise even though the reported CPA stays flat.
What this looks like in an account
The reported CPA is on target. Conversions are steady. The owner says the phone rings less with real jobs. The search terms report shows the best query losing volume faster than the account overall while the worst query holds up. Job numbers in the CRM are flat or falling while the ads report nothing wrong.
We saw exactly this on a windscreen account: account clicks down 20 per cent, the best converting term down 31 per cent, the poorest term down 19 per cent. The mix had shifted toward the cheap stuff because that was the only way to hold the number.
What to do
Give each conversion its real value and switch to value bidding, so the average is now an average of value and junk stops qualifying. Raise the call length threshold at the same time, so a thirty second call is not carrying an £80 value into the new objective. Put the CRM outcomes back into the account so the machine learns what actually closed. And let the budget, not the target, decide how much gets spent.