I have a site that will be an online market places (like ebay)- ie. the site will have buyers and sellers..I need to the buyer to be able to pay the seller directly..and I will need to charge a commission on this.. How can I process payment for this setup?

I could think of 2 solutions - both of which are incomplete for me:
-------------------

1. I could charge the buyer's credit card on my website. And then send the money to the seller. There are 2 disadvantages to this:
------> I will incur 2 transaction charges
------> Since I am making payments to the seller, I will have to report to the IRS when the amount goes over $400.

2. I could see that Paypal is one option for the buyer to send money to seller directly... But, that does not involve the my website at all. And therefore, I will not be able to charge the commission or be notified of the payment.

-------------------
There are so many online marketplace sites..and I assume that there must a easier way out!! I might be wrong with a lot of the above information (researched from the internet) .. Any idea anyone??