I like the Sarakins idea.
Look at current trading/barter system. If you need stuff, you have to go to exact squares on world map, set up tent there and loot stuff from dead members of hostile factions. Then you visit traders, sell all laser rifles, miniguns even with absolutely bad exchange ratio, because you have no duty to care about it, source of this stuff is infinite, only real value you have to spend is time. The only barrier between you and combat armor offered by NPC traders is that somebody else was there before you and he exchanged it first.
I would like to see maybe more advanced mechanism.
I like trading, as a player, you have to detect NPC specialization. You can exchange stuff by best ratio, buy stuff with universal value and resell it where you need, if you dont want to loose value. You have to avoid contact with PK, in hard core areas (like Fortress), you have to create tent network for secure parking place for your car,... . The knowledge about this mechanisms is part of player-trader roleplay evolution.
But i miss trading evolution of your character. Of course, that better barter skill provides you more time for trading, quite better prices, but thats all.
Why not implement Sarakins idea? Maybe even add Combat armors as a requirement, if you want to trade with best barter-armorer. It is logical, who cares about nobody, zero in bluesuit. You as a customer needs to proove that you have serious interest to buy that best stuff.
Also, limitation of access to some traders, like Vault City membership is good idea and it should be expanded. There could exist similar limitation in different places. The idea is that
your trader char, if you want to roleplay trader, will have to expand the source of possible NPC traders. a)
membership to some faction (VC, Raiders, Brotherhood, Enclave)
Like now, i like the idea that you could not have open doors to all NPC traders.
b)
reputation - minimal requirement reputation for some traders (so PK chars could forget about kill and loot their victim and sell/exchange that loot to local merchant)
Better reputation in that locality you have, acces to highest tier weapons/armors you get.
c)
cloth - we have saying in our language: "Je to pravda odveka, ze saty delaji cloveka" - free translation: "this is true, ancient, that clothes makes the man"
ca) "Sarakin's idea"
cb) Robe as prerequisity for special Apocalypse follower (or other religious organization..). I dont mean basic robe, but some special, limited edition
, maybe with limited numbers in the game, or acquired by same way like gauss pistol or car engine part (plus fulfulling other conditions: ammout of trades, level 21, ...). So you will have to be patient before you get this and it will be kind of reward you will get if you get acces to this robe.
Of course, this will attract PKillers, but if acces to merchants via robe will "only" expand your spectre of NPC with PvP stuff, players who dont need to trade this stuff will be more secure. It will attract attention of PKillers, but it means, that their attention would be focused more on this, not on the other, basic traders (theoreticaly).
d)
traveling merchants on world map Merchant parties with stuff that is insuficient in town based NPC barters (because players bought the best stuff). Less stuff in town, more in traveling merchants. As a player, you will have to discover their traveling patches, time of traveling, existance of stuff and this mechanism. You can limit this encounters by setting limitation per real hour for this meeting to avoiding exploits. Also if you will spend running on world map with valuable stuff to trade, the potencial of hostile random encouter and death by NPC is bigger.
f)
quest based (but i know that adding new quest take a lot of work)