Ancients in the Greco-Roman world were, in general, decent at critical thinking about the past, rather than being more gullible than moderns.
For a quick and overly simple example of widespread skepticism,...
Historians like Polybius would say rather explicitly that in their culture 1st hand testimony was the primary way to probe into the past.
This is relevant because Polybius was an expert on the culture.
As one surveys all we know of Greco-Roman culture and their regard for past events, it becomes impossible to deny that they treasured witness testimony above all in trying to ascertain the truth.
This is relevant because it reveals a general Greco-Roman valuing of 1st hand witness testimony when it comes to learning about the past.
Ancients in the Greco-Roman world tended to often quote variations of “eyes are more trustworthy witnesses than ears.” This is relevant because it proverbially praises 1st hand info (seeing vs hearing) while other kinds of info (e.g. old rumor or revelation) were not praised in this manner. And it’s not as if they did not value hearing (or reading).1 So their love of the living voice functions as a fulfilled prediction. While hearing/reading something often meant receiving information merely 3rd , 4th, 5th hand or more, experiencing it 1st hand represented immediate connection with the event or with a witness (his/her testimony) and her authoritative recounting of the event.
Over and above simply valuing 1st hand material more than 2nd hand, and 2nd hand more than 3rd (etc.), Greco-Roman historians around the 1st century tend to find it essentially obligatory that their source-information be 1st hand (or 1st hand as possible). This is relevant because it’s predicted on the hypothesis that testimonies are to be as 1st hand as possible. It’s a coincidence otherwise. For those who allow some lee-way, it clearly wasn’t much.
Regarding most historical works (and writing historical works), there was little desire even among historians for the content to be grounded in 1st hand testimony as far as possible. (See this page to explore.) If true, it is relevant because then all the more lay ancients in general could not be expected to care.
But no, that page also debates 8 counter-arguments: