What should I know before choosing web development services today

I was recently helping a local business owner who wanted to improve his website, and we started exploring different web development services to understand what would suit his needs. Some options focused only on design, while others included full support like testing and updates. This made us think about how a proper website should not only look good but also work smoothly. After seeing these differences, I am now curious, what important things should we check before selecting a service that supports long term growth?