New use for paypal ipn?

I am totally new to oscommerce (and ecommerce in general) so I hope you can be gentle with me. I am contemplating a site which might be able to use your proposed new contribution.It will hopefully have the following characteristics:

1. It will allow many vendors.
2. Each vendor will be able to enter products for sale by him into the master product list which will record the vendor as well as the details of the item via an Administration with Levels module.
3. I hope to collect a fee when the vendor uploads a listing to the product database.

Can Paypal ipn be adapted to allow me to collect the fee in an automatic way in somewhat the same way as checkout allows transfer of money between buyer and seller, only now between vendors paypal account and my paypal account? I would be happy for any help. Thanks.

Albert Hurd