I'm a historian and I recently cited Herodotus in one of my forthcoming papers. Is he reliable? We certainly can't assume so. But the same goes for Thucydides and every other source from the ancient world. It's all about triangulating between different sources rather than relying on any one account.
In my case, Herodotus was describing a Scythian practice (the use of cannabis) that we've been able to corroborate, in its broad outlines, using archaeological finds, which to my mind makes it reliable enough to use.
If anyone's interested, this is a quote from the paper, which is a work in progress and not published yet: When Herodotus described the purification practices of Scythians following elite burials, he wrote of a ritual involving the construction of a tent-like enclosure of “wool mats.” At the center of this enclosure, the Scythians threw cannabis onto “red-hot stones, where it smoulders and sends forth such fumes that no Greek vapor-bath could surpass it.” According to Herodotus, “the Scythians howl in their joy at the vapor-bath.” The term Herodotus used here – κάνναβις, or kánnabis – was a loan-word from Old Persian (kanab). From Greek, it made its way largely unchanged into Latin (cannabis) and from thence into the Romance languages and English." [Citing A. D. Godley, trans. The Histories of Herodotus (Cambridge, MA: Harvard University Press, 1920), 4.74-6.]