First of all, you need to know the technical team level of a professional website production company. The easiest way is to visit the company official website. If a company doesn't do its own official website, I believe it won't pay attention to its customers' websites.
The second is to look at the company's case works. The quality of case works can be judged from visual design, interactive experience and functional realization. Although most people don't know much about technology, they can at least judge whether the website is beautiful or not and whether the user experience is high.
If you are satisfied with all the above, you should know more about the technical team, post-maintenance and so on.