In the original formula the PC level serves as a divisor for the value, determining an item's tier. @BRSamaelhas conducted a series of experiments with high level characters, that clearly show that, once the PC level is over 90, no reachable amount of trading skill is going to yield a tier 15 item, tier 14 items are almost non-existant, tier 13 are met in moderate amounts at extreme skill level(around 1750).
I've altered the divisor, instead of PCLevel+2, it is if((264 - PCLevel)<=100;(264-PCLevel);100)
IMHO, many game developers get it backwards, when they consider the playable character level(or they try to prolong the gameplay on the cheap). The maximum reachable level is effectively game over, sans PvP. So, by the time you reach it, your kit is supposed to be maxed out as well.
Sacred 1 Trading Skill is useful for one thing only - getting items with "% of damage received goes to gold". Otherwise, its utility is,IMHO, nil, especially for the Dwarf with the Thar Eross set.