Recently I got my hands on a copy of Chaosium's Basic Roleplaying, 4th Edition book and am going through it. On page 237, the first of the chapter on "Equipment", under the heading "money", we have the following paragraph:
The “Wealth” section on page 37 provides a general view of money in the game system. A precise set of prices, incomes, and currencies is useless due to the open setting of this game, where prices in dollars, euros, doubloons, yen, pesos, sovereigns, crowns, gold pieces, glass beads, credits, etc. useless for a setting where these are not used. In place of copious currency exchange lists or currency abstractions, the Wealth and Status rules presented on page 37 of Chapter Two: Characters and page 79 of Chapter Three: Skills are utilized.
Further on, on page 239, the book explain how a character with a given Wealth Level can purchase a piece of equipment with a given Item Value, under the heading "Purchasing Equipment":
Assuming that the desired item can be found, the most direct means of handling purchases is through use of the Status skill, described on page 79. To make purchases use the Status skill, modified by these factors:
And then the book lists a number of cases contingent on the difference between the buyer's Wealth level and the equipment's Item Value, requiring checks against the Status (pseudo-)skill in order to buy equipment above their Wealth Level. This is not a bad system, since a Status roll here roughly aligns with how much credit the character has inside the setting and thus can stretch their abstract wealth that much further.
However, the system also presents a skill called "Bargain", which should be relevant in these situations. However, the description of the skill lists the following effects based on the level of success of the roll:
FUMBLE: (...) Items are bought or sold at up to 50% loss (50% cost if the seller fumbles, 150% cost if the buyer fumbles).
FAILURE: (...) Items are bought or sold at up to 25% loss (75% cost if the seller fails, 125% cost if the buyer fails).
SUCCESS: (...) Items are bought or sold at the standard price.
SPECIAL: (...) Items are bought or sold at up to 25% profit (75% cost if the buyer wins, 125% cost if the seller wins).
CRITICAL: (...) Items are bought or sold at up to 50% profit (50% cost if the buyer wins, 150% cost if the seller wins).
Ordinarily, I'd be perfectly satisfied with this explanation, but how do we translate that into the abstract Wealth Levels and Item Values in the Equipment chapter? How much is a 25% profit on the purchase of a piece of equipment of Average Item Value? 50% loss? We don't have even any guidelines to guesstimate, to do that we'd have to know approximately how much more an Affluent character has compared to an Average character, for example.
I guess the Bargain skill could be used to negotiate diplomatic treaties or similar, but that's not really its main thrust.
So my question becomes: Are there any published guidelines or rules explaining how the Bargain skill interacts with Wealth Levels and Item Values, or do they expect a GM to "down-convert" the levels and prices in the equipment lists to some concrete currency before the Bargain skill becomes useable?