Confirmed black holes include Sagittarius A* and the GW150914 primary and secondary objects.
As for quasars, the source region is very compact, mere light minutes in some cases by the constraints from variability timescales. Further, the emission is from very many is obviously from a relativistically orbiting emitter (or otherwise explain the Iron alpha line profiles), so an accretion disk around a massive, very compact object: a black black hole.