What happened to slaves after the slave auctions?

It depended on whether they were bought or not. If they weren't bought, they would be held for the next slave auction, being sold for less, but if they were bought, they would work for their new masters in their new hell life. If they worked for long enough, they were often let go to freedom. They had a document saying that they were free. But all it took was for someone to rip that document up and take them away again, for another life of hell.