Inspect the relevant work
Open three live projects, including one similar to yours. Use them on a phone. Read a long page, navigate with a keyboard and follow the main inquiry path. Ask which parts the agency designed and built; a logo on a client list does not establish the scope.
Ask for the actual team and workflow
Find out who handles design, development and decisions. Ask how feedback is collected, how many review rounds are included and what happens when the scope changes. A clear weekly review with recorded decisions is more useful than a promise of unlimited communication.
Make launch and ownership explicit
Agree on account ownership, source files, content exports and handover. Define the acceptance checklist and the period for fixing launch defects. Keep future improvements separate from correcting work that was already included.