And what global marketplace payment would you recommend?
If you are a marketplace business yourself, you can employ the services of a recognised and regulated payment provider to facilitate payments. Think Paypal used by Ebay. There are a number on the market, it all depends on the precise nature of your business and how you monetise your product. We chose Stripe as it works well for apps and allows us to levy a fee based on the value of the underlying service (we are services driven not physical goods).
It depends on exactly what parts of the transaction you are handling. What you want to avoid is the appearance of or actually facilitating money laundering. Best to consult your attorney or even your accountant and describe the parts of the transaction you will touch and they can highlight the relevant regulations for you.