The verdict
If the shop is the business, I'd pick Shopify. Physical products, stock that has to stay in sync and shipping all need a platform made for orders. If the site is the business and selling is a side feature, I'd pick Squarespace. A consultancy with a portfolio, a few services to book and a small store will have a simpler time there. Shopify's cost creep is real, because apps, themes and payment fees add to the plan. Squarespace costs you flexibility instead, because you work within pre-designed sections. For most small B2B teams selling services, Squarespace is enough. Teams selling products should look at Shopify first.