After playing for a week or so, i have never seen a piece of gear it suggests i sell that is not equipped on one of my characters. Also it has gear upgrades for gear i dont use anymore. Seems backwards to me.
I never sell. I buy as much as I can. Upgrading old gear helps you level.
I sell 99% of the time. Unless it’s an epic or the odd rare I use.
In challenge grinds if the value of the gear will be well more than the gold or gems I take the gear even if I won’t use it.
When you only have a few or a gear it only offers to let you sell 1-3, but as I’ve accumulated more now I’m selling like 10-15 sometimes of commons. So each sale is like 50-75 gold.
Selling all this helps fuel other upgrades, and keeping over 40,000 gold on hand if a good legendary is offered to sale for me again. (It’s been a while, but it happens).
I buy any commons that will give me instant equipment level up. Most rares. All epics and legendary. Sell nothing.
Trust me, before long you end up with way more gear than you have gold to upgrade.
You need to sell some for gold as you get deeper in game.