I think it is important to have an asymmetry between buying and selling: i.e. you can't get a full immediate refund by selling.

I haven't sketched it out on paper yet, but there's something here about time-preference and wanting to incentivize early purchases more than later ones.

Thanks.

The real of reason of **buy/sell** was this person was trying to double sell (but in the UI it shows up a buy/sell, buy/sell). From the software perspective we've fixed the issue of double sell (parallel API attacks). 

mega_dreamer

It's a good first step. I think there might be some more elegant solutions though, that don't introduce as much friction into the system.