What is the current state of the law in relation to unconscionable dealing?

The idea that relief should be available to remedy the harm flowing from an unconscionable transaction has been with us for a long time. In Waters v. Donnelly (1884), 9 O.R. 391 (Ch.D.) at p. 409, Ferguson J. stated: The law which I think applicable to a case of this sort appears to be clearly and briefly stated in a case mentioned by the Chancellor, Slater v. Nolan, Ir. R. 11 Eq. 386, by the Master of the Rolls, and the decision was afterwards affirmed in appeal. The learned Judge said: - “If two persons, no matter whether a confidential relation exists between them or not, stand in such a relation to each other that one can take an undue advantage of the other whether by reason of distress, or recklessness, or wildness, or want of care, and when the facts show that one party has taken undue advantage of the other by reason of the circumstances I have mentioned, a transaction resting upon such unconscionable dealing will not be allowed to stand; and there are several cases to show, even where no confidential relation exists, that where the parties are not on equal terms, the party who gets a benefit cannot hold it without proving that everything has been right, and fair, and reasonable on his part.” This decision does not, I think, lay down any new law but rather appears to state concisely what the law was and is. I think the defendant here has not proved, nor does it, I think, appear that everything was right, and fair, and reasonable on his part. The transaction must have been known to him to have been an improvident one on the part of the plaintiff, who had no proper advise in regard to it. On the evidence and the findings of the learned Judge I think it apparent that he knew he was getting a large advantage of the plaintiff. In that same case at p. 401 it is stated that one first determines whether there was equality as between the parties. If it was absent then a purchaser must establish that the price was fair.