If he's collecting the set, he should have not trouble identify reprints. Reprints will stand out as different to the experienced eye The experienced eye is a sophisticated tool, and people normally fooled when it's an issue they are new to.
However, he and you can also compare cards to ones he already has, as shown below:
Reprint identification through comparison
If you're trying to do a 1956 Topps or similar set in low grade, I don't think reprints is a big issue anyway. I doubt commons and semistars are ever reprinted, and really only the big guns (Mantle etc) is where you should be extra careful.
Also, if you're experienced with an issue, you can usually identify reprints in online pictures too. To seasoned T206 collectors, 99% of reprints and fakes on eBay are obvious just from the pictures. And sellers of fakes will usually use tell-tale fishy language "Unauthenticated, so according to eBay rules I'm selling as a reprint."
eBay has a good return policy and, after you have some 56s in your collection, you should have no trouble identifying reprints once the cards are in hand.