From the text; I believe that Stowe was speaking from the heart.
"Why not make a pecuniary sacrifice? I'm willing to bear my part of the inconvenience. O, Mr. Shelby, I have tried—tried most faithfully, as a Christian woman should—to do my duty to these poor, simple, dependent creatures. I have cared for them, instructed them, watched over them, and known all their little cares and joys, for years; and how can I ever hold up my head again among them, if, for the sake of a little paltry gain, we sell such a faithful, excellent, confiding creature as poor Tom, and tear from him in a moment all we have taught him to love and value? I have taught them the duties of the family, of parent and child, and husband and wife; and how can I bear to have this open acknowledgment that we care for no tie, no duty, no relation, however sacred, compared with money? I have talked with Eliza about her boy—her duty to him as a Christian mother, to watch over him, pray for him, and bring him up in a Christian way; and now what can I say, if you tear him away, and sell him, soul and body, to a profane, unprincipled man, just to save a little money? I have told her that one soul is worth more than all the money in the world; and how will she believe me when she sees us turn round and sell her child?—sell him, perhaps, to certain ruin of body and soul!"