Don't Hold Me To It! Where Contractual Intention Overrides Statutory Conditions

Section 14 of the Ontario Sale of Goods Act ("SGA") imposes the term in all purchase agreements that goods sold will match their description. However, section 53 of the SGA allows contracting parties to "choose their own adventure" by contracting out of the implied term, but only when they expressly agree to do so. But how stringent is the standard for proving "express agreement"? How does the specific wording of an exclusion clause balance against the surrounding circumstances and the parties' intentions? Finally, how should vendors and purchasers word exclusion clauses to best protect their interests?