In most cases, the IRS requires two things to consider an expense valid - a receipt or other record showing what the expense was for and a credit card statement, canceled check or other documentation proving you actually paid for that expense. Otherwise, in addition to faking receipts, people would just pick up receipts off the ground/out of the trash/etc.
Pretty good idea, though - the guy behind the site has to be making great cash, considering you can buy a USB receipt printer new with the software needed to design the receipts he shows on the site for $150.