It's just as provable as a loan in the first place.
If the person hasn't sent the agreed amount, and they have enough in their account and alt to compensate the loan and meet the profit requirement, then a TSA should send the TC up to the profit mark. If they don't have the TC, compensate with items to meet the profit mark.

It's just another form of generating income, it's already hard enough to do, limiting options for no reason seems just.. bad taste. Enlighten me if there's actual reasons behind it that this suggestion doesn't cover