People could theoretically put their reto .onion onto their profile or sign it with their pgp key and then you can search for it in the client.

Iv noticed some people may choose to mention their past personas on the other platforms. Or it could be someone just pretending, unless they provide their public pgp key how would you know until you trade with them and you recognise address? Trust no one. Prepare to lose a small amount in the mail as tests at fist or use other methods on haveno which if you deal with a scammer could be worse.

anyone could use any names. I think such a system would not have positive consequences

Not that I'm aware of, there is absolutely no reputation system in the program other than onion address.