Like any product, buy early, buy high to rip/flip
buy later, buy for less, to keep or rip/flip
Rip and flip and eventually you will lose money on any product unless you get super lucky.
The thing about Sportkings is the player will not drop in potential or stature, well maybe an OJ Simpson, but I think that increased his value, like a Brien Taylor, Joey Harrington, Stromile Swift and more (I know that's going way back, I'm sure the mainstream sport collects have better examples)
There are still many great cards to be pulled and promotions also.
So I just bought a 16 box case