Ask: will this site sell, or just describe?
There's a big difference between a site that describes a company and one designed to convert a visitor into a customer. If your goal is sales or leads, you need to make sure whoever builds it actually understands conversion, not just visual design.
Ask about speed before you ask about looks
A site that looks beautiful but loads slowly loses visitors before they see anything. Site speed has also become one of Google's most important ranking factors — so it's not a cosmetic detail, it's a direct commercial one.
Ask: will the site be easy to update?
If every small edit (changing a price, adding a service) means calling the company and waiting and paying, that will cost you time and money long-term. Ask directly: after delivery, will I be able to edit it myself or not?
Ask about support after delivery
Every website needs ongoing maintenance and updates. A good company tells you clearly what's included after delivery and what needs a separate agreement — before you discover that the hard way when something breaks and nobody answers.