GDPR Article 14
The provision of Regulation (EU) 2016/679 that obliges you to inform people when you obtain their personal data from a source other than themselves, as a rule within one month.
It is written for exactly the situation scraping creates. At the scale of a classifieds site — roughly 107,000 private sellers on coches.net — the obligation cannot be discharged, which is why the defensible engineering answer is not to collect the field.