Perhaps the guy declined (politely) because of the profiteering that occurs in other collectible fields. Joe Baseball signs something for a fan and the object ends up on eBay for $$$. Autographed chips appeal to only to those who specialize in signed chips, a small but friendly market. There may be some cross-collectibility but mostly I'd guess an honest mistake on Mr. Pepper Person's part on the actual value of his scribble.