B737 Captain reported refusing the aircraft after the reason for a hydraulic leak was not addressed correctly.

Narrative

We had brought the aircraft from ZZZ that morning and landed at ZZZZ. A passenger had mentioned he saw a dark fluid coming from the wing of the aircraft. Upon do the walk around I did see fluid dripping from the aft part of the wing near the fuselage as well as from the fuselage. Also I observed a large streak along the fuselage trailing aft of the wing which appeared to be Hydraulic Fluid. This fluid was definitely not any form of deice fluid. The hydraulic gauges read 100% on the A side and 91% on the B side. They were both full that morning before departing ZZZZ.I wrote it up and Company Maintenance had a local Technician come to inspect. The Technician showed up and agreed we had Hydraulic Fluid leaking from the aircraft. He had us cycle the flaps and speed brakes several times. No new leaking was observed. Company Maintenance signed off the plane as OK to continue since the leaking could not be replicated. The First Officer and I discussed the matter for some time and I concluded I was not going to fly passengers on this aircraft because no explanation could be given to me as to why so much Hydraulic Fluid had leaked from the plane. I refused the aircraft at that point.