Seller offers to sell Buyer a boat for $500. Buyer replies, “I think I want the boat, but let me have a week to consider.” Seller replies, “OK. I won’t sell the boat to anyone until after one week from today.” The next day, Seller sells the boat to Popeye for $600. The day after that, Seller says he has already sold the boat. Nevertheless, Buyer tenders $500. a. Is Seller contractually liable to Buyer? b. Would you answer change if Seller were a merchant and his promise not to sell for a week were in writing?