1. All loom POINTS are of the same value
2. Value and price are different things
3. When looming an item you turn the loom point to something different
4. This different thing, the loomed item, now has both a value and a price. Those things are not the same in almost any case, and the BASIC value also changes according to the usefulness of the item. As a pickaxe is better in almost any aspect than a cudgel, looming a cudgel lowers the value you have, in ANY case.
5. Prices are also determined by other factors like supply and demand, popularity, looks, etc.
In simple: you and your work mate earn the same salary. After a month both of you earn the same wage, which means you have the same value. He invests all of it into real estates, you invest all of it into used toilet paper. Although you were able to buy several tons of it, your wealth was reduced with that really bad purchase, while his wealth stayed the same. Having paid the same price for both things doesn't mean they have the same value.
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Just implement an automatic "trust" function. Once a trade has been confirmed, the trading goods are "frozen" for 24h. Within this time each trading partner can cancel the deal again and get his items back, as does the other one, of course. 90% of all problems with the marketplace solved. You're welcome.