1. Conversions are not set up or are broken. The algorithm optimizes for what gets measured. With no purchase data, Google brings "clickers" instead of buyers. This is mistake #1 by a wide margin.
2. The ads lead to a website that isn't ready. Slow, no prices, a clumsy mobile cart – you pay for the click, and the website "loses" the buyer. Ads amplify a website; they can't make up for its flaws.
3. Broad keywords without negative keywords. Your ads show for "free", "DIY", "used" – the money goes to an audience that never planned to buy.
4. A store without Shopping campaigns. Pouring the whole budget into search ads while ignoring Shopping/PMax with photos and prices means paying more for traffic that is less ready to buy.
5. Feed problems. Disapproved products, outdated prices, "in stock" on sold-out items – half of the catalog simply isn't advertised, and you don't even know it.
6. The price is noticeably above the market. In Shopping, buyers see prices side by side. If yours is 30% higher with no explanation, you get clicks (curiosity) and no purchases.
7. The campaign was paused during the learning phase. For the first week or two the algorithm is learning, and results are unstable. Pausing it "because it's expensive" on day 5 throws away what you have already invested in learning.
8. No remarketing. 97% of visitors don't buy on their first visit. Failing to bring them back leaves the cheapest orders to your competitors.
9. Calls and messenger chats aren't counted. In many niches, half of the orders come by phone or Viber. Without tracking them, the ads look worse than they are and get cut by mistake.
10. "Set it and forget it". A campaign without regular search term cleanup, tests and adjustments degrades within months. Advertising is an ongoing process with no single button to press.