Raising my hand as another new player, coming from other games (like WoW, SWTOR, etc.) where loot is classified and categorized differently, and therefore handled differently by NPC / game vendors (not player owned vendors).
I think the basic issue here is that new players (like myself) don't understand what 'junk' really means in SWG terms, because the natural inclination is to assume 'junk' means 'trash' or 'useless' and therefore we should sell it. It's not SWG's fault we have that assumption, there are a great many other games that set that expectation and reinforce it with 'sell all junk' and 'sell all trash' buttons, because in those games that is how you make money at low levels.
So what do we do? How do we help new players understand that 'junk' in SWG is not actually 'useless'?
I understand we have player built resources in the wiki and with guilds. But the first interaction a new player has with the game is the game itself, when they first start, get sent on their starter quest, and start killing enemy NPCs and collecting loot, which includes junk. There is absolutely no indication in the game of what is valuable to keep vs sell.
Furthermore, the included Prima Guide PDF (which is a fantastic resource, BTW) does not cover this distinction either. Or if it does, it's not in the obvious sections of Junk Dealer or Looting.
So I recommend a few different options:
1) change the name 'junk' systemically, game wide, to something more intuitive -- this has many many implications to the entire game, so I don't know what the appetite is for this
2) make a prominent section in a new player guide -- like the Prima Guide PDF -- that explains what 'junk' really is and is not, and how to think about it when managing inventory and deciding what to sell
3) as for 'sell all', given the above, I wouldn't limit it to a particular category of item, but instead force the player to select what category of item they want to filter and sell -- junk, armor, weapon, component, etc., the same categories used in the bazaar. You cannot complete the transaction until you select a filter.
Just some thoughts and a different perspective of what the real problem here is, to me. Thank you for your consideration