We rebuild the page closest to your sale and run it against the one you have now, on your own live traffic. The scoreboard is revenue per visitor, not a dashboard metric.
Usually the product page, because that is where the money is decided. We rebuild the page with the highest leverage rather than spreading small edits across the store.
Old page and new page run at the same time on your traffic, so seasonality and ad spend hit both equally. The result decides, not an opinion.
Two or three tests a month after the rebuild, each one measured the same way, so the page keeps improving instead of settling after one win.
Fewer opinions, more tested changes: if the rebuild does not lift revenue per visitor, you keep your money.