Sexologist Visits

A middle aged married man and a married woman were having an affair and wanted to get a room, but the hotels were asking for $200/per room even for a short time; so they ended up going to a Sexologist Doctor and said that they had a sexual issue and they wanted him to watch whilst they did it. After it was over Doctor said they were quite okay and presented a bill for $100, which the man quickly paid it. This went on for quite some time as they went to his clinic every week. Ultimately Doctor couldn't resist anymore and asked them why they were paying $100 to him every week when their was perfect and both of them had pleasure at the same time within 10-15 minutes.
The man responded, "Doc, the hotels here charge $200 whereas you only charge us $100 with a bill for your consultancy which is accepted by the insurance company who also reimburse us $85; so I'm only out of pocket $15 and both us have pleasure without any problems at all".
Doctor replied, "Okay please carry on as long as you wish, but stay out of trouble".