Bad to bye a runt pup?

im getting a pup that is the 2nd pick of the litter, there was 8 male pups all together. there is one runt they call it that is about 1/2 the size as the other pups, shes selling it for alot cheaper than the rest of the pups too. when i saw the picks i fell in love with the little guy, and am thinking of bringing him home too. what do runts turn out to be? is there any problems prone to these dogs? does that mean they are not as smart? please stick to the question....