For the most part, there is nothing technically wrong with a 2nd that would affect the performance of the ball. 2nds can include:
porosity (small pits in the shell)
engraving error (stray lines on the logo, etc)
color issues (half/half balls, extreme phasing)
high top weight
pin-cg-mb offset
2nds are no more prone to cracking or core separation or anything like that compared to firsts. The biggest issue people will see is finding an acceptable layout for them if the top weight is too high or the pin-cg-mb are way too far out of line.