Treasure value house rule

Treasure is a big thing in OSR-type games. It's the incentive for going to dungeons, and the main source of XP (in gold = XP systems). So eventually, when the PCs leave the dungeon and go back to town, all the various non-magic items (gems, jewelry, artifacts, whatever) are converted to their respective base monetary value (as set by the DM / the adventure's author).

A good way to retain flavor is using a house rule:

The players can opt to "go the extra mile" when converting treasure to XP. They designate up to 5 items from their loot as "significant artifacts". The DM doesn't have to disclose the base value of the artifact. Then roll 2d6 for each item separately on the following table:

2	The item has no value or won’t be bought by anyone for some reason (superstition, disgust, prejudice?). No gold or XP is gained for it.
3-5	The item is sold for half its base value. XP is halved.
6-8	The item is sold for its base value. XP as normal.
9	The item is sold for its base value. XP as normal. However, the buyer is ready to pay double for the next identical or related item (but that item will still grant XP as base value).
10	The item is sold for its base value. However, the buyer shares a piece of historical or arcane information related to the item (+20% XP)
11-12	The item is sold for double base value. XP is doubled.

Optional rule: if the roll is a double (e.g. two 3's), in addition to the effect, the PCs attract the unwanted attention of a local criminal organization, tax collectors, other adventurers, etc.