I talked about this previously, but my views on top selling items have changed in the decade since I released my Merchandise Forensics booklet.
Best selling items are more important today than they were ten years ago.
Best selling items used to be "best". What is "best" is now channel-dependent and seasonally-dependent. What works on Facebook is different than what works on Google, and what works on Google is different than what works via Email.
Best selling items historically were either margin generators (a $100 item with an $80 gross margin) or unit hounds (a $10 item with an $8 gross margin selling 10 units). Now that marketing channels are playing a much bigger role among winning items, the $40 item with a $32 gross margin selling a handful of items is important ... to Google or Facebook.
We're going to change our definition of winning items going forward. The high margin item that brings in new customers but doesn't appeal to loyal customers is still a winner ... we'll just define "winning" differently.