Instead of double clicking then hitting enter for each equip you're NPCing, click on the first equip in your inventory, then hold down "Y" while spam clicking the "Sell item" button on the top right. (Make sure you check the stats of all the stuff in your inventory before doing this & to not have anything of value, because it goes very quick. rip ~buyback)
Alternatively, if this doesn't work on your computer, you could move the pop-ups (one is the main selling/item pop-up and the other is the confirmation of sale pop-up) so that they overlap each other and then just spam click to sell quickly. I like to put the confirmation box in a position where the "yes" is right above the third item on my list, so that I can just spam away without really thinking about it.
