How do I calculate the value of items?

I admit, I put myself in this situation. I created some unique, non-magical items for my PC (with a lot of help from folks on this site). I assumed he would want to keep and use these items, but he has decided that, because they're so unique, they must be valuable, and is trying to sell them. One example is a loose "camouflage" tunic that provides +2 to stealth in forest environments.

My attitude is: if the PC wants to sell the items, that's great! This is his adventure. But it has presented me with the issue of determining these items' value.

I don't think this problem is necessarily specific to my unique items, either. At one point, my PC rolled a natural 20 perception check on a meaningless pile of rocks in a meaningless cave. There was nothing worth perceiving, so I said he found a hunk of unrefined gold jutting out of a rock. I wanted to give him a little reward for the natural 20 (and I'd rather not debate that, because I like to reward 20s and penalize 1s), but how much is the hunk of gold worth?

The question is, how do I determine a fair value for items that I can't find in the D&D items and equipment list? So far, I'm trusting my gut, but it leaves me wondering if I'm being fair to my PC. Any thoughts?

(Update: I really appreciate everyone's answers so far, but responses have been focused on the two specific examples I gave [the tunic and the gold]. I'm looking for general guidelines/thought processes that I can apply to any item that doesn't match anything in the D&D list of equipment. The two I listed were just two examples. Sorry for the confusion. Thanks.)

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The general 4e assumption is that mundane (non-magic) items are either not sold at all, or are sold at 20% of value. So you could theoretically fiat that the tunic cannot be sold. However, lets think about this loosely within the confines of the game's mechanics.

Ask yourself the following questions

• If this were a magic item, what level, rarity and type would it be (by type I mean major item or consumable).
• What mundane items resemble this item

If you can answer the first question then this should give you your answer fairly quickly, price them at a level that is appropriate for the powers they grant (that tunic is actually fairly close to the existing camouflage clothing that costs 30 gp, although of slightly less value, so price it below that).

The ore is a bit trickier. My suggestion would be that you have them find a smith or refiner to haggle with Have an idea in mind of what the value is and start the Smith's price lower and have them use their cha based skills to try to get him up. Settle at or around your target value (tweaking for rolls obviously).

Finally, because I just thought of it, Mordekainen's magnificent emporium brought in some new mechanics for trade goods that give some help to DMs for players looking to sell goods. It might not fit exactly but it could be helpful for setting some base lines.

Buying and Selling: To perform either of these transactions, establish the total value of the trade goods in question. Use the major purchase column on the table in the Pocket Change entry to figure out the level of this transaction. For example, unloading a rare book worth 10,000 gp—or a forged copy of the same—would be a 15th-level transaction. Use this information with the Difficulty Class by Level table (Rules Compendium, page 126) to determine the DC to sell or buy a trade good, or to recognize or pass off a fake item.

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My suggestion would be that, whatever value you give your gold/cloak/etc, it comes out of the Treasure Parcels (see the DMG) that you have set for the heroes. This way you can set your prices without too much worry, as the heroes won't become 'rich beyond their level' from [crafting cloaks]/[gaming the system].

In the DMG there are examples for valuations of Art, this can also be used as a rough comparison for whatever exotic items you are using in your game.

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A hunk of prospected gold is probably worth X*Y% of its weight in gold coins, where X is 0.7 to 0.9 depending on how popular the local coinage is, and Y is what % of the coins' purity the chunk has (i.e. if the chunk only has 70% of the purity of gold that the coins do, the chunk would be worth X*70% of its weight in gold coins).

As for the unique items, look for a magical item that gives a similar benefit and price it about maybe half the sale value of that item (because magic is expensive). Isn't there a cloak that gives a stealth bonus? Calculate the value of the stealth bonus (i.e. subtract the price of a basic Amulet of Protection with the same plus to NADs), then halve it for only giving its bonus in forest environments, then halve it again for not being magic.

EDIT: Since wax eagle was nice enough to look up the camouflage clothing, we can use that as an example. Things usually sell for 20% of their purchase cost (assuming you're allowed to sell them at all; not usually the case for non-magical gear), so the camouflage cloak would sell for 6gp in a game where the GM was nice enough to let someone sell it. I'd say half that since yours is a conditional bonus, so 3gp.

Also, never give this player any cool stuff ever again if he's just gonna hock it at the first pawn shop he comes to.

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wizards.com/dndinsider/compendium/… this is the camo you're talking about – wax eagle May 4 '12 at 3:48
sure.Its camouflaged clothing. And its listed in Dragon 373 p22 and Mordenkainen's Magnificent Emporium p124 – wax eagle May 4 '12 at 3:57
Ha! You're right, I shouldn't give him anything else, but it's a duet campaign. My Pc is traveling alone and needs some cool stuff to allow him to survive. When I tell him what he can get for the gear he thinks is super-valuable (3gp), I'm guessing he'll have second thoughts. Thanks for your response. – Lechlerfan May 4 '12 at 5:06