WanderOne says:
Could the GM give us an ideal of...the ability to sell magic items and how much that might bring?
Selling items involves:
1) finding a buyer. With many common items (such as weapons), this will be very easy and there are many possible buyers. With rarer items, there are probably fewer people who want to buy them, and some of them might be willing to buy for a lower cost.
2) Arriving at a sell price. The NPC will make an offer, which the PCs can accept or try to negotiate. This negotiation could be strictly role-play, or it could involve mechanics if you want to haggle quickly without so much conversation (this would be a CHR (Persuasion) check).
3) Making the sale.
More about sell prices:
The value of mundane items should be fairly clear, though the offer price may differ based on whether the person wants it for themselves (usually a higher offer) or they want to resell it (usually a lower offer).
The offer for most common items (such as weapons, armor, etc) will usually be
less than the normal purchase price for a new item of that type (a beat-up, old glaive is perceived to be worth less than a shiny new one), while the offer for rare or unique items might be
more than the purchase price of a comparable new item (an heirloom medallion, or a historical statue).
Magic items are interesting, assuming you can find a buyer. Some people will buy
unidentified magic items on the hope that it's something good; this may mean that the offer price is much lower than the actual value (if it turns out to be a beneficial magic item) or much higher than the actual value (if it turns out to be a detrimental/cursed magic item).
Identified magic items will sell for much more money than nonmagical items (of course, you might not want to sell them if they're useful to the party), but identifying the magic item requires someone casting
Identify, and if that person is an NPC, that costs money, too. Still, it's likely that even a single common magic item will sell for more than enough money to cover the costs of training one or two Dungeon Busters.