There are few players slashing atm and most of them have their gear quite complete, even if some came back after the last (nice) updates. Almost no new players around.
Kake is right in the point that you have to pay the fee when setting it on the MP - before you in fact sell the item. You lose the fee for nothing in many cases.
Also ppl are unsure about the prices, they have been decreasing but still perf/close to perf items sell relatively expensive.
For that reason a vendor tries to find a buyer first by offering the items in the tradeforum and put it on the MP when he has a serious player according with his price suggestion.
So if you need stuff, open a iso topic or check gear of active players and pm them directly if they are willing to sell.
The trading for medium stuff is so down that many slashers stopped even using the vault : The 100 fg per 30 days wont easily come in by the drops ... thats the status quo.
Good luck