Keener, et al. often refer to the gospels as more consistent about Jesus than other sources are about the figures they discuss or how the gospels are superior to other ancient sources in some other manner:
Synopses of the Synoptic Gospels suggest, at least where we can test Matthew's and Luke's adaptations of Mark, that they may treat their sources more conservatively than Philo treats the biblical life of Moses (i.e., more like Suetonius than like Philo)....
Soo-Kwang Lee's essay on biographies of Arrian notes that most scholars regard Arrian as our most reliable source concerning Alexander [the Great], even though Arrian writes centuries after Alexander's death and at many points must decide among radically inconsistent reports. This is partly because Arrian depends on some sources from the period of those who knew Alexander. By comparison, the Gospels also stem from the period of those who knew Jesus, and are much more consistent on key points such as the manner of Jesus's death. (32, 38)
John Jordan Henderson's chapter on inconsistencies in Josephus (including inconsistencies in his autobiographical material) is especially striking. Critics of Christianity often rely a lot on Josephus, frequently citing him against the gospels and other Christian sources in various contexts. Yet, much of what's in Josephus is more problematic than what they're criticizing in Christian sources. I've written about some of the problems with Josephus and the use of his material by critics of Christianity in other posts, like here.
Critics often object that the gospel authors report events that they supposedly couldn't or probably wouldn't have known about (e.g., Jesus' conversations with Pontius Pilate). How would the gospel authors have had access to such information? But the authors of the book I'm discussing sometimes note material of a similar nature in ancient non-Christian biographers and historians (165-6, 195).
John Jordan Henderson makes a good point about a contrast between how people often approach the gospels and how they approach ancient non-Christian sources:
Richard Burridge, among others, has argued that our focus, as we study the Synoptics, should be on the subject of the biographies - Jesus - rather than on hypothetical communities supposedly responsible for creating them....
For instance, Michael Grant writes regarding Suetonius' biographies, "It is only from Suetonius that we get a plausible idea of what sort of people [the twelve Caesars] were" (Grant, "Foreward," 10). He does not posit a community that read its experiences back into the lives of the Caesars, then assert that in reading Suetonius' work, all we can really know about is this community. (261, n. 2 on 261)
Some of the more ignorant skeptics of Christianity object to appeals to fragmentary Christian sources, like the fragments of Papias' writings preserved in later sources. But Keener, et al. often refer to similar reliance on fragments in the study of ancient non-Christian biographies and other non-Christian sources (e.g., 201).
It's also common for critics of Christianity to ask why the sources Luke refers to in the opening of his gospel, the writings of Papias, and other such sources weren't preserved. Why would the ancient Christians have preserved so many later writings while not preserving so many earlier ones? I've discussed that issue in depth elsewhere. Keener and his colleagues provide examples of how ancient non-Christian sources likewise often preserved later sources more than earlier ones, gave more attention to later sources, etc. (e.g., 204-8) Those non-Christians probably had reasons for doing so similar to the ones I outline in my post linked above. As I mention there, we often do the same thing in the modern world.
Critics sometimes object to the fact that Jesus didn't leave us any writings. But that was common practice in the ancient world. Keener notes that:
Many teachers left the matter of publication to their followers. (340)
Just after making that comment, he goes on to make another good point on a different matter:
Occasionally students left their philosophic traditions and disagreed with their former teachers, but if they disagreed they said so, rather than falsely attributing their own views to the teacher. (340)
There are some brief responses to alleged parallels between Jesus and figures like Apollonius of Tyana, Sabbatai Sevi, and Simon Kimbangu (34, 351).
(Upcoming segments in the series will be linked here when they become available: part 4, part 5.)