Any recommendations of firms/teams that can develop a fully featured ecommerce website such as Jumia?

I've got an idea for an auction website, so the end product should have features such as user registration, bidding, order placement, etc. I'm NOT looking for simple web design companies.

I would look for teams on sites such as elance, but I'm not sure how they would go about integrating payment options such as Mpesa.


Cheers,
Daniel