Andy Geldman has written a nice piece on the third party marketplace seller. Increasingly, this is the way to startup online for a variety of reasons but in particular due to customer/traffic opportunities and things like third party fulfilment. The elephant in the space is offcourse Amazon though others are entering the space.
As Andy says:
Those sales are made not by Amazon themselves, but by more than 2 million independent businesses – businesses which are largely hidden from view.
Read more at Pulse