Building a marketplace - which one is better a unified registration or two separate ones?

I'm currently building a marketplace. And need to decide whether to:

• Have two separate registration forms - one for the buyer and one for the seller


• Have a single registration form and then when a user is registered he/she will need to choose what role they want to take (buyer/seller) and will be required to fill additional details relevant to each role

I'm asking this mainly in terms of user experience as I think that there might be a chance that a user will want to function both as a buyer and a seller (though it will probably happen only in 5% of the cases, most will function only as one).

Answer

Why would any user want to have two separate accounts?

If you ask me, I want one login for everything on the internet (and still retain control over my privacy, thank you).

You would build artificial hurdles. I'm a seller, and see something I would like to buy. Do I have to log out, log in with my new "buyers" account, find that product again?
Do I have to use a different browser if I want to monitor my sales while buying?
How many buyers will give up selling and go to ebay if they are overwhelmed by the separate account?

You are not enabling new functionality Any user wants to buy and sell through different accounts can still sign up with separate accounts.

Usability

Any decent UI can comfortably support both buying and selling. Even if you insist on completely separate interfaces, the choice can be made after login and remembered as default for that user - making it a once-in-a-lifetime click,

Build for easy transition. Your power users - those generating the most business - are the most likely to do both. Do you want to penalize your cash/click-cows?