You'll have to explain that to the Israeli intelligence services, which surveiled Gaza Health Ministry staff (e.g., listening to their phone calls) and determined that they were working in good faith.

Just because the governing political party carries out terrorist attacks against Israel, that does not mean that literally every institution in Gaza is unreliable. The IDF carries out war crimes all the time and is known to be extremely unreliable,[0] but there are still many institutions inside Israel that are reliable.

0. There are way, way too many examples of this to list here, but I'll just highlight one. The IDF attacked a convoy of Palestinian ambulances in Rafah, killing almost all of the paramedics. When this came out, the IDF put out a statement claiming that the ambulances were actually being used as a cover for Palestinian Islamic Jihad and had approached an IDF position with their lights off. Then, a video surfaced of the incident, showing that the ambulances were flashing their emergency lights, and that the paramedics were unarmed and had been gunned down by the IDF. It also came out that the IDF had subsequently buried the ambulances, in order to try to hide the evidence. In other words, the IDF committed a war crime, tried to cover it up, and then concocted an elaborate series of lies that they put out for public consumption: https://en.wikipedia.org/wiki/Rafah_paramedic_massacre.

It's very convenient to assert that literally nothing that goes on within Gaza is knowable, in exclusion of any other facts, "because Hamas", but you're not actually engaging with the reality that external validation and corroboration can still exist.