In the financial industry, face-to-face conversation is an essential for sales. Similar to call-center monitoring, there is a significant need to monitor the conversation for compliance checks. In certain business scenarios, there is a need to record an employee's speech while protecting the customers' confidentiality and privacy. In this paper, we propose a small-scale microphone array system specially designed to record only the agent's speech. For the suppression of the customer's speech, we used CSP-based post-filtering. However, using small number of microphones, it is difficult to suppress unwanted speech completely. Because post-filtering using correlations of the multiple channels often affected by the spatial aliasing between speakers. We introduced the weighted-CSP to attenuate susceptible bins to the interfering speaker. Also we introduced flooring after the post-filtering to mask residuals. This combination helps prevent the customer's speech to be transcribed.