Client influence on property valuation has been an emerging theme of behavioural research in the real estate discipline. Studies on valuers’ decision-making behaviour imply that client influence is an important source of judgemental bias. Academic interest in client influence research has evolved from identifying the existence of client pressure to studies that explain the mechanism of client influence. A questionnaire survey was administered to valuers to measure their perception with regard to factors affecting client influence in Malaysia. The effect of client size and size of value adjustment requested by clients on valuation were also tested in a behavioural experiment. The survey revealed that valuers in Malaysia perceived client characteristics and valuer characteristics as some of the most important factors affecting client influence on valuations. It was found that factors such as type of client, size of client, integrity of valuer and experience of valuer could potentially impact on the amount and type of influence exerted on valuations. The results of the logistic regression model indicated that neither the client size nor magnitude of value adjustment requested by client affected the decisions of valuers to alter valuation outcome.