Orientate yourself to the SHS rule:
✅ Question: Change your perspective: Take on the role of the other person. Why is the buyer or seller acting the way they are? For example: Why would someone sell an item that is in high demand at particularly favorable conditions?
✅ Protect: Have you noticed something suspicious or suspect attempted fraud? Report suspicious processes or users to the relevant platform.
You should also file a complaint if you have been the victim of fraud yourself.
Detailed tips and information can be found on this police advice page: https://www.polizei-beratung.de/themen-und-tipps/sicher-handeln/die-shs-regel/