In Jesus' day, Nazareth was a no account town, an unimportant village. More than that, it seems to have been the idiomatic examplar of such - as they say, can anything good come from Nazareth? In South Africa, we have similar small towns with this function, being Pofadder and Putsonderwater here.
As it was an unimportant place, there isn't much extra material about it from other sources. There is no reason to doubt it existed though, as we are looking for a tiny village, and beneath the modern town remains from back then can be found.
The reason some people make this claim, is because Jesus of Nazareth is such an historical detail, that it messes with those that want to claim Jesus is a euhemerised archangel or the like (the Christ Myth crackpots). They need to explain away Nazareth, to explain away Jesus of Nazareth's historicity; so they opt to say the name was ascribed later or so. This is a fringe idea of an already fringe group though, as even most Christ Myth adherents admit Nazareth was a place back then.
