A rule that bans a bidding strategy does not ban the arithmetic underneath it.
An account I went through this week was running Maximise Conversion Value on a target ROAS, because a house rule had banned target CPA outright. Sound rule. Never buy traffic the business cannot afford. Except every conversion action in that account carried a value of 1. A phone call, 1. A form filled in at midnight by someone who then went to bed, 1. And a target ROAS of 0.05 on a value of 1 is a twenty pound target CPA. Not similar to. Identical to.
The banned strategy had been running since the middle of the month with a new name badge on.
Here is the part that should sting. A webform lead in that business is worth about seventeen pounds. Roughly one in eight turns into a job, and the average completed job is a hundred and thirty four. So the bidding was cheerfully telling Google that twenty pounds a lead was fine, and on the second campaign, sitting at 0.02, that fifty pounds was fine. Fifty for a seventeen pound thing, on autopilot, for over a week.
Nobody decided that. It fell out of the maths while everyone admired the label.
The machine was not misbehaving. It was serving a till that rang up every lead at the same price, so off it went to find more of whatever was cheapest to ring through.
The fix was not the bidding strategy. It was giving the conversions real prices. Seventeen on a form. A hundred and fifty on a phone call, because someone who rings you at ten on a Tuesday morning is not the same animal as a box that got filled in.
A target ROAS is not a strategy. It is a ratio, and a ratio with the same number on top of everything is just a spending cap in a better suit. Put a real price list next to the till, or the machine will keep buying the cheap ones, and they are cheap for a reason.