What is the test for establishing a presumption of undue influence in a real estate transaction?

In Goodman Estate v. Geffen 1991 CanLII 69 (SCC), [1991] 2 S.C.R. 353, Wilson J. stated: 42. What then must a plaintiff establish in order to trigger a presumption of undue influence? In my view, the inquiry should begin with an examination of the relationship between the parties. The first question to be addressed in all cases is whether the potential for domination inheres in the nature of the relationship itself… 43. Having established the requisite type of relationship to support the presumption, the next phase of the inquiry involves an examination of the nature of the transaction. When dealing with commercial transactions, I believe that the plaintiff should be obliged to show, in addition to the required relationship between the parties, that the contract worked unfairness either in the sense that he or she was unduly disadvantaged by it or that the defendant was unduly benefited by it. From the court's point of view this added requirement is justified when dealing with commercial transactions because, as already mentioned, a court of equity, even while tempering the harshness of the common law, must accord some degree of deference to the principle of freedom of contract and the inviolability of bargains… 45. Once the plaintiff has established that the circumstances are such as to trigger the application of the presumption, i.e., that apart from the details of the particular impugned transaction the nature of the relationship between the plaintiff and defendant was such that the potential for influence existed, the onus moves to the defendant to rebut it. …the plaintiff must be shown to have entered into the transaction as a result of his own "full, free and informed thought". Substantively, this may entail a showing that no actual influence was deployed in the particular transaction, that the plaintiff had independent advice, and so on. Additionally, I agree with those authors who suggest that the magnitude of the disadvantage or benefit is cogent evidence going to the issue of whether influence was exercised.