Although bartering can be good in a game, I would really not enjoy having to find something specific to trade for what I want. This kind of system would make me buy stuff from the trader even less than I already do. And it would absolutely get me to spam quests even more rather than less. Instead of buying anything, I would just quest and scavenge instead of spending time trying to find the right thing and then remembering which items to carry with me to buy that thing.
And then it makes traveling to other traders even worse because now you don't know what they want to trade for to get what you want and traveling there to find out, only to either go back to base to get the items or spend time scavenging until you find them near that trader. It just doesn't sound very good to me.
And when it comes down to it, bartering without requiring specific items isn't really any different than what we do now. You can buy stuff with money, but if you are selling as well, then it is like you are bartering. You are just not doing the buy/sell at the same time. I could see maybe adding in a UI box for buying and selling at one time like other games do. Just not requiring a specific item or items to get each specific thing you might want to buy.