Over the past 23 years I have built online credit card processing architecture for Ticketing systems many times.  We have always tried to allow the organization using our system to choose their own merchant provider so they could negotiate their own rate with their provider of choice and be not locked into a system where someone is bleeding a percentage off every transaction.  I am not a big fan of Quickbooks but I often quote the fact that they publish their rates and anyone who pays a swipe rate greater then their sub 2% rate is being robbed.

In the early years we had no choice but to go directly to the merchant service provider over a modem and sending the data in a proprietary format.  In the mid 90's we switched to using a middle-ware software such as PcCharge or Southern Data Com.  Now merchant providers have caught up to the internet and are providing direct web services interfaces that are capable of handling thousands of simultaneous requests.  We wrote a Patron Edge credit authorization system 6 months that talks directly to these merchant providers and have found great success in processing many simultaneous transactions.