Unable to use MarketPress to have a global shopping cart and charge a profit

When reading threw your website I found that you have MarketPress and one of your support reps was telling someone you could have users have their own accounts, and sell things using their own paypal account then you could use PayPal chain to make money off it and have a global search and shopping cart on the main site and the buyer would have a smooth shopping experience with one checkout. Upon activation of this plugin I have found if you want a global shopping cart you can not use PayPal chain which means I can not charge a fee on the sales that take place. Is there a way to make this work or is MarketPress not able to allow me to make an Amazon like store with buyers and sellers?

Thank you for your time and help.