the 30 second rule while trading with a merchant makes it impossible to check the dets of every weapon you want to buy. this way you may be sure that you have bought a det 0% gun.
Barter timeout is based on your barter skill. If you have barter skill 30 points you have 30 seconds, with 100 points it would be 100 seconds.
Anyway this is too short to check status of every weapon (or just check the stat of this particular weapon on the bottom of the list, many many clicks away),
while it is annoying to wait for another char finishing trade right now.
Auto-Discharge and Auto-repair would speed up bartering enormous, it would also increase ammo supply and make weapon crafting more attractive, because weapon prices would rise significant (because they all have 0 det.)
There are only 2 drawbacks figured out so far
1. No realy cheap guns from merchants for self repair
2. Ingame logic problem: Why should a bartender be able to repair a weapon?
Of course it would be possible to have only gun/armor traders auto-repairing weapons and armor,
while bartenders, brahmin traders and other NPCs just have them auto discharged.
Their inventory is actualy not that much crowded.
You could still buy cheap detoriated or broken weapons from those NPCs, or from other players (or loot them).
This would perhaps boost P2P trading. I´m not sure, but I guess those Übersoldiers out in the wasteland seldom have repair skill >150.