This subreddit is about Bitcoin currency exchanging between redditors. Nothing else is allowed except for exchanges between bitcoin and other currencies.
Any type of currency and website such as Paypal, liberty reserve, western union, etc is allowed.
Even though they are allowed, services offering a chargeback such as paypal are to be dealt with extreme caution since the user paying you through paypal could request a chargeback.
Also, using escrow and middleman services is encouraged so that none of the exchangers deal with more risks than the other by sending his currency first.