Is it possible to charge a percentage/flat fee upon sale of posted item rather than charge for ad post? If yes, is that built into the latest version of the script?
No, this is not a built in option that is currently available. Whether is possible for someone to customize it to work this way, I guess depends on your coding skill.
I think it is not so on what you are suppose to because tax rate may be adjusted annually according to a formula based on balances in the unappropriated general fund. The different tax policies is not allowing to that.
