I responded to this post on another thread. My experience with Mercari has been positive. The only issue I've encountered is that their system doesn't always detect tracking when the item has been shipped, but it always updates once the item has been delivered. Then they contact the buyer to rate you. If the buyer doesn't rate you in a few days, Mercari releases the money automatically. The time between when the package is delivered to the money hitting my bank account is usually less than 5 days, sometimes only 2 days. It is cheaper than ebay because there are unlimited free listings and no paypal fee.
I also wish there was a way to organize listings. Maybe there is and I haven't found it.