There is no good way to avoid getting a CAPTCHA except to just browse and shop normally.
Google analyzes multiple factors to determine if they may be using tools to try to accelerate checkout. This is based on services they are logged into, their mouse movement patterns on the page and many other items that are not published. Google does not publish their methods because people would then be able to get around them.
Learn more about reCAPTCHA here - https://developers.google.com/recaptcha