Want to understand procedure

Greetings,

I came accross a trend in business where people provide Fake purchase bills. Charge for such invoice is 50% of Vat amount mentioned in bill. The buyer saves on VAT as he claims 100% amount mentioned on bill as exemption.

How can some one provide Proper Tax Invoice at 50% of Vat amount.How does the seller of Invoice make profit?

I wish to understand how this system Works.