That invoice scam is why big companies have such complex expense report systems. They need to verify every transaction is real so they can match up real invoices to. I'm more or less trusted to buy $5000 worth of stuff at a time (number is somewhat random, but this covers most travel expense). However they still need to check because if they just pay all bills someone will send a bill in my name (easy to find out a name of someone who works for a company - my name would be chance, but likely enough) even though I didn't buy anything in the companies name.
