Start with the portfolio, not the pitch
Any agency can describe itself as professional. A live portfolio of real, working websites tells you more than a sales call. Open the actual project links on mobile and desktop, check loading speed, and see whether the design looks current or dated.
Pay attention to variety. A company that has only built one type of website (for example, only restaurants) may not have the structure needed for ecommerce, logistics, or service-based businesses with more complex content.