No. Your actual cost-per-acquisition (CPA) depends on factors outside Google's control, so it's possible that your actual CPA may exceed your maximum CPA bid in CPA bidding campaigns.
The AdWords system uses historical conversion data to predict the likelihood your ads will convert. However, your actual conversion rate can be affected by changes to your website and ads, or external factors such as increased competition. If your actual conversion rate turns out to be lower than the predicted conversion rate, your actual CPA may exceed your maximum CPA bid.
Also, the likelihood of your actual CPA exceeding the maximum CPA bid increases if you only use CPA bidding for a short period of time. The system is designed to adjust over the long term, with the goal of avoiding any conversion with a higher cost than your maximum CPA bid.
