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.)
Best Answer
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 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.