I agree that Sir T could have given Tom a smaller allowance, or, after he went into debt, have cut off his allowance. However, I think many people back then pretty much lived on credit. Tom would not need cash in hand to purchase clothing or saddles, he could just charge them, and the tailor or whoever would just send the bills to Sir T. And I think the only way Sir T could have put a stop to Tom's doing that would be to publish a notice in the paper that as of such and such a date, he would no longer be liable for Tom's bills - a step that would have been pretty drastic and would look very bad for the family.