Hi James,
Basically you work for virtual pounds (Barter Pounds) so if your clean is £75 you 'earn' B£75 to be redemmed against a product beneficial to yourself, i.e printing is the great example reps use.
However, even though against Barter rules if you order printing etc many firms simply double the price and say ''i'll do it 50% Barter''.
Also for Barter to make money it costs you something like 5% in cash for them to authorise the deal.
I know the guy very well who had the brokeridge in York, now closed down.
Bargepole springs to mind.