I like the vending of this game,
To sell something, one needs to spend some resources on it, either the need to pay or the need to keep your computer on are good. This prevents sellers from trying to vend useless/overpriced items which would flood the market.
In that sense, having something like paid Offline Vend Scrolls or a system that charges a set % of zeny when putting up an offline vend even if items aren't sold would be great.
Although great, they are probably not simple to develop/test/implement .