[newunderwriter007]

if merchant signed for 100k pay back 140k and only received 6k . now he stacks and owes 140k for only receiving 6k. how can he pay back that much for receiving that little

Not the way it works. To use your example, the contract only covers a MAX of $100k which can be funded under the contract. If at any point the contract is killed, because of stacking, negative days or the merchant saying they doesn't want it anymore, all the merchant owes is the payback of the amount they received, minus what they paid back. The problems kick in because all the existing pulls have to be paid out of the merchants own resources, plus the pull of the reverse which has to be paid off.