@_Meh_:
I'm trying to recall how Alvida came by the Sube Sube no Mi, and I don't remember that it was ever stated. So, here's my theory:
First of all, does anyone else remember people in East Blue mentioning the sale of humans? Higuma the Bear mentioned that he might sell Luffy, before deciding to kill him instead. Nami told Luffy that he might be sold off by Buggy. So, right there you have two mentions of slavery way back in East Blue. This brings me back to my theory.
The first time we saw post-DF Alvida, her crew was nowhere in sight. In Buggy's flashback, it was mentioned that Devil Fruits could sell for as much as one hundred million Berries. Is it possible that Alvida sold her own crew to amass enough money to buy a Devil Fruit?
Sure, nice theory I like it.