Can a vendor who is late in signing a contract with a third party who has been late in entering into the contract, take advantage of the other party's performance?

The law precludes the vendor from taking advantage where he was responsible for the later performance of the other party. The parties to a contract have an obligation of good faith that compels them to honestly conclude a bargain that has honestly been made. This obligation extends to prevent a suddenly reluctant vendor from reneging on improvident bargains by relying on minor technical breaches. If the late-tendering party can show that the delay is attributable to the other party, their right to claim specific performance is preserved: see Minto v. Jones, [2008] O.J. No. 3687 (S.C.). …