(b) That's right. In some relationships, a general controlling influence by one person over the other is not presumed. However the weaker party may be able to prove that such a general controlling influence actually exists, in which case, it is then presumed that a transaction entered into on the advice of the stronger party is the result of undue influence. The dominant party must then prove that the transaction was not the result of undue influence, failing which the transaction may be set aside as void.
The relationships which give rise to this possibility include: husband and wife; principal and agent; accountant and client; banker and customer; dentist and patient; and employer and employee.
In the present case, the relationship between A and B is one of accountant and client. To have the transaction set aside, B must first prove that A had a controlling influence over his (B's) decision-making. The facts suggest that A does have a general controlling influence over B, at least in relation to B's financial affairs. Accordingly, a court will presume that A used this influence improperly and the transaction will be set aside as void unless A can prove that in fact he did not use his influence improperly.