I think they have a few models for selling, mostly based on an estimate to the number they can sell.
Contact owner of product, ‘we can sell XX of your product at £yy price, for which we want zz%’
or
Owner of product ‘I have surplus of product you can have at fixed cost of £y’ to which sport-pursuit then list at whatever price they think they can make maximum profit on an effort / sales / profit-per-item ratio.
They never handle stock as far as i can tell, just middle men giving us access to deals in one location. Its becoming quite a popular business model with the rise of internet shopping, its good for smaller companies that might not have the reach/presence/advertising budget to draw enough customers to their own websites.