You can only opt-in to someone's €ddie$ if you meet them or whoever rightfully received their €ddie$ in person or if it's a business you trust.
Best practice is to let someone id themselves before you opt-in to their €ddie$.
It's also adviced to let someone make a bank transfer to you, to add another layer to their id.
Not everyone has a id or bank account, so be cautious and use others or your own judgement to proceed.
If you weed out people who doublespend, scam, steal or have a bad reputation, that contribute to your own rep. Every feedback must be presented with proof of facts, costing 1 €ddie$ per proof. €ddie$ can also be loaned to proof a fact.