What do you mean by "trust", what's your threat model? Tailscale does way, way more than just facilitate key exchange. If tailscale.com goes down or rogue, you're still in a pickle even with PSKs; just because there's a Wireguard under the hood, doesn't mean you can swap an API endpoint and continue as if nothing happened.

Even with self-provided PSKs, you're going for an (IMHO) pretty poor trade-off; keys, certificates, etc should be regularly rotated, that's a chore that's best left automated. At that point, why not just set up Wireguard yourself?

If you have legitimate concerns, you should be using Headscale[1] (or even plain Wireguard) from day 1. Otherwise - personally I find the current threat model very reasonable, it's in no way worse than trusting any other VPN provider, and they're keeping a pretty big chunk of their code base open for auditing.

[1]: https://github.com/juanfont/headscale