Before you switch agencies, check who owns what
Switching is straightforward when your accounts are yours and painful when they are not, and that is settled at setup rather than at the exit.
What should I check before switching?
Whose name is on the domain, hosting, Google Business Profile, analytics, ad accounts and phone number. For each one, could you remove your current agency's access today without asking them?
What usually goes wrong?
The domain and the Google listing. Losing either is genuinely disruptive, and both are commonly registered by an agency during setup as a convenience nobody revisits.
How do I leave cleanly?
Get ownership transferred before giving notice, ask for an export of everything in writing, and agree a date access ends. Doing it in that order removes almost all the friction.