A lot of it has to do with who is the seller. There are numerous reliable sellers who know how to identify raw reprints. If you're buying a raw 1933 Goudey Babe Ruth from a guy with 2 feedback, you're taking a chance.
Side by side a reprint or counterfeit and the real card from the issue are usually distinctly different in multiple ways (thickness, gloss, stock color, other). Even if you only have some T206 commons, you should be able to identify a fake T206 Honus Wagner when you compare in person. Commons, stars and Wagner were were made the same way, with the same type of ink and card stock. Same theory and practice applies to Willie Mays and Dan Marino Rookie Cards.
A collector, even an experienced collector, is most likely to be fooled when buying from an issue he's never owned or has experience with. He has nothing to compare it the questioned card to, not even memory. On the other hand, if you've collected 1971 Topps since, well, 1971, a reprint will stand out like a sore thumb.
My printible
pdf guide shows how to make such comparisons (what to look for), along with other topcs concerning identify counterfeits of early cards.