Think It's Click Fraud? You Might Want To Think Again
For example, a high bounce rate/low average time on site could be attributed to click fraud, but it could also be a symptom of a mismatch between a highly descriptive ad and a generic or even irrelevant landing page. Meanwhile, low conversion rates could be symptoms of an overly complex or broken shopping cart.
Sometimes a high volume of traffic from the same IP can be seen as a sign of click fraud, but a simple WHOIS lookup could reveal that an ISP is kicking out multiple visitors from one address. Brazelle also touches on why advertisers just starting out may see what seems like excessively high CPCs, as well as incurring traffic from non-Google sites when they've clearly opted out of the content network.