An actual barter system, using the ‘bartering’ skill, might be nice, using probablities for striking (or failing to strike) a deal. The lower chance there is to strike a deal, the greater the XP reward.
Level 0: The player has to pay 0-200% more for an item, and receive only 10-50% of the normal value upon sale, depending on the bartering skill of the NPC.
Level 1-4: ???
Level 5: Strike a successful deal with 95% probability if the items have the same trade value (up to NPC bartering skill 8; with 9 and 10 you still have to cough up 10% and 20% more respectively). Player is unable to rip off low-skill NPCs.
Level 6-9: ???
Level 10: Get 25% discount and/or get 25% more value out of your sales, as long as NPC bartering skill is 5 or less. Ability to blatantly rob low-skill NPCs in trade (most of them, right?). Ability to start Ponzi schemes? Or a new wasteland-wide stock market exchange?
This would mean that there’s some or decent incentive to learning at least the basics. You could try to offer sucker deals, such as offering a worn sock for an assault rifle, but if the NPC refuses a deal 3 times in a row, he/she stops trading with you for 3-7 days, thus probably preventing any cheap exploitation attempts. Any glaringly bad deal will instantly result in a similar “ban”… for a full year. Also, you shouldn’t be able to offer the same identical deal twice in a row if the deal is initially refused. Possibly have the ban lifted with a successful speaking skill check.
After that it’s just a matter of correcting item prices, one glaring injustice at a time. After about 20-50 such corrections, we might have a semi-decent bartering scheme.
Also, we might make each NPC accept only certain items (categories) in trade, instead of NPCs being willing to buy anything and everything.
Thirsty NPCs might pay extra for drinks (quench).
Hungry NPCs might pay extra for food (nutrition).
A sick NPc might pay hugely for proper medication.
If an NPC is wielding a gun, its ammo caliber could be a more valuable commodity to that NPC.
Furthermore, upon world creation, certain items or categories (listed in a separate file) could have abnormally higher or lower prices (applying modifiers), in an attempt to randomize the economy a bit for each game. Could come as a mod, too. It wouldn’t have to be permanent for each game, so the wasteland economy and trends could also fluctuate, and each year or season the item price modifiers in the list would be randomized again. NPCs and traders might provide hints (or direct info) about which items or categories are trending this season. Or the NEXT season. Such information could be obtained with the speaking skill, thus creating some synergy between the two skills. Either that, or upon closing a sizeable deal, the NPC reveals the current or future trends.