I think this is a very valid question. For me, the undeniable fingerprint of Gulenists is the fact that police chiefs dismissed for affiliation with Gulen were caught inside the military tanks. There are videos of it and I don't see any other logical explanation for catching suspicious civilians in military vehicles during a coup.

For people who followed the last 10 years of the Turkish politics, the Gulenist affiliation is obvious but I think it is still very hard to explain it to people who are exposed for the first time. Before Erdogan, the Turkish military was actively cracking down on the Gulenist infiltration and it is 40 years old subject with hard to believe but proved multiple times conspiracies.

Gulenists always abuse the benefit of doubt and as a secretive cult usually the evidences against them have some kind of explanation and all these strange coincidences are tagget as normal. After all, there is nothing stopping the Lottery from winning on the 1 2 3 4 5 6 numbers every time, its just improbable so it is not 100.000000% guarantied to be fraud.