Unless you've got millions of pounds to provide stocks of your products to everyone involved in your scheme, the only way it can work is if participants buy their stocks from you (or other participants) and then sell them on to others. i.e. participants will have to pay some money 'up front'.
That has an important legal significance because it's illegal to take payments from others to join a scheme if the principal 'selling point' of the scheme is that they'll make money from recruiting others (rather than by actually selling the products). Running a 'pyramid scheme' where people are told that the main way they'll make money is by recruiting others (and where the participants have to pay something to join the scheme) is a serious criminal offence, which can lead to a lengthy prison sentence.
Before proceeding further, make sure that you know the law:
http://www.berr.gov.uk/files/file24757.pdf
Chris