We rebuild the page nearest the purchase and run it head to head against the one you use now, on your own visitors. Judged on revenue per visitor, not opinions.
We rebuild your highest leverage product or landing page. Usually the product page, because that is where the money is decided.
The new page runs against your current one at the same time, on the same traffic. The result decides, not the argument.
Two or three tests a month after the first win, each one measured the same way and kept only if it holds up.
Product page rebuilds and ongoing split testing for ecommerce brands, with every figure measured on the brand's own traffic.