I have two rare karma daggers, two fine accessories and two masterwork accessories. What is the use of these items? They're all low level (the highest is the daggers at 40).
There's not a huge amount you can do with these after you "outgrow" them, apart from:
- deleting them (throwing them away)
- sticking them in the Mystic Toilet (as BlackVegetable suggested in the comments, any other weapons should do, or, if you want to get a dagger out, put four daggers in; similarly for trinkets), ideally on a day where you get credit for that in the dailies
Otherwise, there's no point keeping them and you can't sell them to vendors (because you can't get karma from a merchant, and if they gave you coins for it there'd be a way to directly convert karma to gold, which ANet wouldn't want) or salvage them (because you could then sell those proceeds, which ANet wouldn't want). With the recent update, you don't need to keep them for transmuting their skin either, because the skin has been automatically unlocked on your account when you logged that character in after the update.
You can use the mystic forge to get some random other thing, or just delete them. I basically throw away low level gear after it get's "outdated". There is not end game use for it. The only items worth something are level 80 yellow+. The rest... salvage if possible, mystic forge (I have bad luck so I prefer salvage), or destroy.
You raise pretty fast in level (especially if you craft) so most items will become (unfortunately) useless quite fast.