Though this might be helpful to validate offers, I feel this would be tedious and unnecessary. Some already ask for proof, but at the end of the day, the consumer will pay what he/she is comfortable with paying, there's never any obligation. While it is a form of deception on the seller's part if they lie about it, it is a marketing tactic after all. The ever so famous "buy low, sell high" ideology itself was built on taking advantage of an opportunity and exploiting it for your own benefit.