Why will the servants that the king has sold be returned, according to Huck?

From the text:

A couple of nigger traders come along, and the king sold them the niggers reasonable, for three-day drafts as they called it, and away they went, the two sons up the river to Memphis, and their mother down the river to Orleans. I thought them poor girls and them niggers would break their hearts for grief; they cried around each other, and took on so it most made me down sick to see it. The girls said they hadn't ever dreamed of seeing the family separated or sold away from the town. I can't ever get it out of my memory, the sight of them poor miserable girls and niggers hanging around each other's necks and crying; and I reckon I couldn't a stood it all, but would a had to bust out and tell on our gang if I hadn't knowed the sale warn't no account and the niggers would be back home in a week or two.