Proof of Purchase? What Proof of Purchase?

This from The Roto Times weekly notes column: "Just for fun, let’s take a look at Adrian Beltre’s 2004 April and April of this year. 2004: .353 BA, seven HR, 20 RBI. 2006: .189 BA one HR, 6 RBI. If only the Mariners had kept the receipt when they gave him that $64 million deal."