Ted accurate response addressed the question from a Seller and Listing Broker's perspective, in relation to their exclusive contract.
A cancellation clause in a purchase agreement is a clause that details the conditions under which each party may terminate the agreement. It appears to me that you may be confusing "Contingencies" with "Conditions" ... A Buyer has contingencies which enable them to cancel the contract within a specified and negotiated time period. "Conditions" are used in the lending arena, prior to funding the Buyer's loan. If you are only in the "offer" stage of the contract, and NOT in escrow or have a fully executed contract, then the Buyer may withdraw their offer, using a CAR Form WOO. If you are not in default and want to cancel the contract, use the CAR Form CC, Cancellation of Contract, Release of Deposit and Joint Escrow Instructions.
If you are a seller and in escrow with an executed contract, the only condition which allows you to cancel is if the Buyer is in default or if the Buyer should initiate the cancellation. Good luck on your transaction.