Leak one: broad match without a negative list
Broad match will find you traffic. It will rarely find you customers unless you tell it what you do not want.
Review the search terms report weekly for the first month and add negatives aggressively. This single habit usually saves more money than any bid strategy change.
Leak two: search partners and display expansion left on
Both are enabled by default on many campaign types and both quietly spend budget on placements you would never choose deliberately.
Turn them off, run for two weeks, and compare cost per conversion before deciding whether to reintroduce them.
Leak three: conversion tracking that counts the wrong thing
If a page view counts as a conversion, the algorithm will optimise towards page views. Track submitted forms and connected calls, not visits.
Also check you are not double-counting: one enquiry recorded twice makes a losing campaign look profitable.
Leak four: one landing page for every ad
If the ad promises a specific service and the page opens on a general homepage, most of that click is wasted.
Match the page headline to the ad headline. It is the cheapest conversion rate improvement available.
Leak five: nobody is looking at it
Accounts left on autopilot drift. Competitors change bids, seasonality shifts, and a keyword that worked in March quietly stops working in July.
Thirty focused minutes a week beats a four-hour panic once a quarter.