It depends on where your head is, and what your level of skill happens to be.
You could actually run something like BitEscrow, and integrate it into your site. Or you could run a full on copy of Bitcoind, that would do the job without a payment processor. Of course, that requires thinking about things like security, which you might not want to do.
On the other hand, you have services like Coinbase and Bitpay and Coinpayments, and others, that can take some of the risk away by offering a viable third party interface, for which they, rather than you are responsible.
It also depends on the bigger question; which is, do you want to have Bitcoins or Fiat at the end of the transaction cycle? If it were me, I would want Bitcoins, because I like Bitcoins. But your needs may be different. You very well might want dollars or euros, and that's okay too.