1. Only US dollars are used for pricing.
2. The integrated payment methods are Paypal and Stripe which means they will show on the site automatically when the order has been paid instead changing them manually to paid on the site and payments are automatically split for multiple sellers. Like if you buy x from John and y from Sallie then you only pay 1 time and Paypal or Stripe will send the right amounts to each seller. Other payment options listed are bank wire, check, and GoogleWallet so pretty much anything. I could add an "Other" option just to put the details of different payment methods.
3. The seller needs to have an option to accept payment but it doesn't have to be US dollars. I'm tagging items to search for the payment method(s) so buyers can search for items for how they want to pay (e.g.
https://digitalassetmarket.me/search?tag=Stripe).
4. The buyer and seller transact directly. This is one reason in mind why member verification is so important. An external escrow service could be used and is recommended.