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 sale is decided. One page rebuilt properly, not a list of small tweaks 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.
Two or three tests a month against the winning page. Fewer opinions, more tested changes, with each result written down.
It suits Shopify and direct to consumer brands with enough traffic for a test to reach a clear answer in weeks rather than months.