I think this is available to those who are subscribed to GGE.

Percival Green (US1) said:

In Equipment please place a button next to the Mark Favorite Equipment Mode button.  Call it something like Group Sale.  

When I click that button, it says “Sell All” and then gives the following list with a button for each: Common equipment, Rare equipment, Epic equipment, Legendary equipment, Common-Rare equipment, Common-Epic equipment, Common-Legendary equipment, Gem 1, Gem 2, Gem 3, Gem 4, Gem 5, Gem 6, Gem 7, Gem 8, Gem 1-4, Gem 1-8.  You click the button and it asks “Do you want to sell all your (your choice) which is not assigned to a commander or castellan?”  If you then click yes it sells all of that equipment.  

Example: I click the Equipment icon, and then click the Group Sale button.  I click from the list the button for Common-Epic equipment.  It asks me “Do you want to sell all your common, rare, and epic equipment which is not assigned to a commander or castellan?”.  I click yes.  It then sells all of my unassigned common, rare, and epic equipment.

This 2018 thread asks for the option to click "sell all of the same quality" while selling a particular piece of equipment: https://community.goodgamestudios.com/empire/en/discussion/comment/4969996#Comment_4969996
I wanted to make it as simple to program as possible, while placing it next to your new Mark Favorite button in Equipment.

flug (NL1) said:

Percival Green (US1) said:

In Equipment please place a button next to the Mark Favorite Equipment Mode button.  Call it something like Group Sale.  

When I click that button, it says “Sell All” and then gives the following list with a button for each: Common equipment, Rare equipment, Epic equipment, Legendary equipment, Common-Rare equipment, Common-Epic equipment, Common-Legendary equipment, Gem 1, Gem 2, Gem 3, Gem 4, Gem 5, Gem 6, Gem 7, Gem 8, Gem 1-4, Gem 1-8.  You click the button and it asks “Do you want to sell all your (your choice) which is not assigned to a commander or castellan?”  If you then click yes it sells all of that equipment.  

Example: I click the Equipment icon, and then click the Group Sale button.  I click from the list the button for Common-Epic equipment.  It asks me “Do you want to sell all your common, rare, and epic equipment which is not assigned to a commander or castellan?”.  I click yes.  It then sells all of my unassigned common, rare, and epic equipment.

This 2018 thread asks for the option to click "sell all of the same quality" while selling a particular piece of equipment: https://community.goodgamestudios.com/empire/en/discussion/comment/4969996#Comment_4969996
I wanted to make it as simple to program as possible, while placing it next to your new Mark Favorite button in Equipment.

the solution is already there.

if you buy an subscription  you cab select with a button that equipmen will be sold automatticly