I don't know what the situation in Germany is, but as I only ever hear about those issues from the US, I assume its something ridiculously bureaucratic, which might actually be a plus in this case?

So in Germany, you need to prove your identity to buy a SIM card. You can't really buy an anonymous phone, because every SIM card is tied to someone's identity.

This probably doesn't prevent SIM swapping entirely, but you will need to also steal the other SIM card you're swapping the number to.

Ah, I guess I forgot about that. Yeah, you either need to intercept the new SIM sent to the original customer, or defeat the identification procedure. That adds quite the hurdle compared to countries that have no such requirements.

At least for now you can still easily anonymously buy (activated) sims from other european countries.

But I think you can't use those for taking over a number in a SIM swap.

According to the linked [0] report, of the two providers in Germany that were asked, one had 1-10 incidents, and one 11-30. In a year. So I guess those issues exist, it’s just a minority issue. The related German Wikipedia page [1] and almost all articles I can find also mainly talk about the USA. It seems you can usually add another required password for phone changes, but mainly it’s just not an issue. No ridiculously bureaucratic requirements, though.

[0]: https://www.enisa.europa.eu/publications/countering-sim-swap...

[1]: https://de.wikipedia.org/wiki/SIM-Swapping

Whereas currently your google account can be taken over without any social engineering at all.

No, just require them to answer their phone. Charge a fee if necessary.