Start with relevant references. A large gallery means little if the examples do not demonstrate content clarity, responsive behaviour, performance, and the kind of business complexity your project needs.
Ask who owns strategy, content, design, development, analytics, SEO, and launch quality. Projects suffer when these responsibilities are fragmented or silently passed to the client.
Clarify the technology, hosting, source ownership, licences, security, backups, editing experience, documentation, and post-launch support. These decisions determine the real operating cost of the website.
Finally, ask how success will be measured. A credible partner should connect design decisions to qualified enquiries, sales, adoption, search visibility, editorial efficiency, or another observable business outcome.