I will (hopefully) clarify once and for all what my colleague Gion already tried to.
NOBODY force you to FREELY give your credits to ANYONE from game, doesn't matter what they promise you or not. The moment you agree to give someone something FOR FREE (without using the market as it is intended) you're on your own risk.
If a random guy does tell you give me x money I'll give you x things and you do that, you're basically begging to be scammed.
Thanks to the scammers, they are actually HELPING in changing the buyers mentality from "credits only" to actual game currencies or combinations of game currencies and credits.
When there are no buyers that want to RISK being scammed then there won't be any more offerts in "CREDITS ONLY", due to no buyers left to take the risks.
You passed our limit? You deserve to be scammed, end of story.
And no, there won't be any shitty rule about this, SCAMMING is the way to fix the mentality, not shitty rules that still can be avoidable and won't fix the real issue (any1 that can agree to bypass the rule can simply tell us they moved credits from an account to another or simply gift them to guild mates / friends and move on).
And no, limit will never be higher than 500 credits, which is high enough anyway, but due to the "inflation" of credits gained from game it does look like a "low" limit.
My personal advice for buyers and sellers that wants to have a safe economy without scams while keeping the prices the same: use credits for jewels and jewels for credits, simple as that. Let's say you want to sell an item for 1000 credits:
Calculate the value of jewels in credits, put the price in jewels, sell the jewels for credits, for the same amount.
If people does learn to use market in this way, there will be only benefits for everyone in the market, including players with low amount of credits and people that don't wanna risk being scammed.