How can I get money back if the payment has not been paid?
If the payment was not successful (for example, it was canceled by the author or moderator), then the funds will be returned to the wallet of the user who transferred the funds.
If the user paid for the purchase in real currency (USD, EUR, RUB or others), the funds will be returned to his ETH-purse inside the CoinPlace system.
This seems like a solid concept but it wont have a good chance to work. Its all well-known, I have had similar projects in the past and can tell that all that crap is just for eggs. Its nothing more than a rip-off from other few hundreds fiat -crypto gateways, and none of those third-world centralized services could last more than a week or two.