Cash Back brings more sales ? – Affiiate Products with Cash Incentive allowed

For example ABC payday loan Lead $30 which allows cash incentive and You decide to pay $10 cash back to customers.
And you state in your site "$10 cash back,provided customers present you the proof of purchase".
I have never this before even if cash back is allowed and wondering HOW EFFECTIVE IT IS.
Could someone post your experience?
Statement of cash back offer in your website sells 2 times more or 3 times more than your promotion without cash back statement?
OR
The same or Negligible sales increase?

See original post by herok