Generally speaking if a specific product sells a lot, it's safe to say it's a good indication that it's pretty good. And if you're wondering what those items might be, according to this recent report from B&H, here are some of the current Top Selling Products in various categories.
Top selling camera- far and away:
Top selling Lenses:
Top Selling Tripod
Gitzo 100-Year Anniversary Edition Tripod with Ball Head
Top Selling Continuous Light
Aputure Light Storm LS C120D II LED Light Kit with V-Mount Battery Plate
Top Selling Studio Strobe
Profoto B10 OCF Flash Head
Top Selling Camera Flash
Godox AD200 TTL Pocket Flash Kit
Computers drives and storage:
Simple – 8TB for $139.99 WHOA!
WD 8TB Elements Desktop USB 3.0 External Hard Drive
and a close 2nd: