Maybe you can see this as a scam, too. At many places (not all) guides get cheaper tickets for attractions. For Example they will ask you for the regular price of 60RMB, but then they buy the ticket for just 10RMB.
They didnt earn this difference themself, they have to give it to the agency their work for. A friend of me is a guide, so I know this very well.
But I dont think you have a choice to refuse it. You can try to buy your own ticket, but then you have to pay the full price at the ticket counter so you didnt win anything.