Drain surgeon plumbers not picking up obvious leaks in a unit

My tenants in Kemptonpark informed me their unit is flooding. I called drain surgeon to come and fix the leak. I accepted the call out and first hour work for around R1600 which is more than the normal call out fee but I accepted it since I decided to work with a franchise which I can keep accountable.

The plumber informed me that they do not know where the leak or the water is coming from and that I will need to utilize their leak detector services which will be an additional R1800 including vat, this was after they spent around 10 min in the unit. I agreed since the assumption is that it is somewhere in a wall and concealed and the leak cannot be determined with the naked eye or with standard tests. Soon as the leak detector arrived I was told that the bath is cracked and the washing machine draining into the bath is flooding the unit. So I was given a quotation to replace the bath. So I need to pay for the leak detector and if I do not accept the quotation I will have to pay for the call out and first hours labour as well and absolutely nothing has been done do far. I am concerned if plumbers working with these kind of things for a living walk into your unit spend 10 mins cant find a leak and recommends a leak detector when there is a major crack in the bath with the washing machine outflow running into the bath!!