Data cannot be used for other than the purposes outlined initially. For example, taking an email address at the time of booking and then using it, without further consent for E-mail marketing or to pass data on to third parties like Tripadvisor is not allowed.
=== How do I obtain consent to process my privacy policy and to processing of personal data?===
Consent needs to be explicit, opt-in, and freely given. You can achieve this with a custom question with a link to your privacy regulations which you can set these up in SETTINGS->PROPERTIES->BOOKING QUESTIONS.