Experiments on the effectiveness of relevance feedback with real users are time-consuming and expensive. This makes simulation for rapid testing desirable. We define a user model, which helps to quantify some interaction decisions involved in simulated relevance feedback. First, the relevance criterion defines the relevance threshold of the user to accept documents as relevant to his/her needs. Second, the browsing effort refers to the patience of the user to browse through the initial list of retrieved documents in order to give feedback. Third, the feedback effort refers to the effort and ability of the user to collect feedback documents. We use the model to construct several simulated relevance feedback scenarios in a laboratory setting. Using TREC data providing graded relevance assessments, we study the effect of the quality and quantity of the feedback documents on the effectiveness of the relevance feedback and compare this to the pseudo-relevance feedback. Our results indicate that one can compensate large amounts of relevant but low quality feedback by small amounts of highly relevant feedback.