Ask what happens after launch
The build is the easy part. The relationship afterwards is what determines whether the site still works in three years.
Ask specifically: who hosts it, who updates it, what it costs to change something, and how quickly.
Ask to see something live
Not screenshots. A working site you can open on your phone and click through. Try to book something on it, or enquire.
Anybody can produce a flattering image. Very few will hand you a live URL and invite you to break it.
Ask how they will make you findable
If the answer involves buying ads, that is a different service. Ask what they do about search visibility as part of the build, and whether it costs extra.
If local SEO is an upsell rather than a standard, you are being sold a brochure.
Ask what they would not do
A supplier who agrees with everything is not thinking. The useful ones will tell you a page you want is a bad idea, or that a feature will not pay for itself.
That is the person you want when you are spending money.
Ask about the exit
Nobody enjoys this conversation, which is exactly why it is revealing. What happens if you want to leave.
The right answer is that you take the domain, the content and the site with you.