pretty sure you are just an aggregator. Visa & MC are making this more 'feasible'
All of our merchants get their own merchant account during our onboarding process.
Admittedly, it's a complex process behind the scenes. We know that a lot of people are interested in how we do this, and we want to be completely transparent about our business practices. We plan on putting out a blog post explaining it all in detail in the coming weeks.
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Here was my best attempt: http://news.ycombinator.com/item?id=2445866
If your blog post could cover all the components I tried to cover there--but without the errors I probably made and with the gaps filled, I and many others would be grateful and ecstatic.