Understood, thought that might be a possibility, but won't the high outlay be a barrier to entry?  For the uninitiated, I could see how putting 100% on the line would make them uneasy or irate for a variety of reasons.  In many, many cases it would be entirely impractical.  The folks using these marketplaces by and large won't be rich.  Their net worth could (and in practice, will be) tied to the very items they're selling.  For the guy listing the 10,000 BAY comic book, that could be an entire month's salary locked up in crypto limbo until the sale is completed...an amount our fictional seller cannot afford to put aside.

Is there any way to incentivize the deposit and reward completed transactions?  For example a lottery wherein one could yield anywhere from 0.0000001% to 10% of the deposit for a sucessful transaction?  There are a variety of interesting ways to implement the odds of high payout, to further incentivize good and civil conduct.

The BAY to fund such a system would have to come from somewhere...where I don't know...but I believe it will take more than 0% fees to overcome aversion to 100% collateral.

Just kinda spitballing as I really like this project and want to see it succeed.