You have no right to use pictures of another person for your commercial benefit (e.g. marketing on your website) or pictures you took for pay (since the intellectual property rights to photographs done as "works for hire" belong to the person paying for them), unless and only if there was a written agreement allowing you to sue them. So you are in the wrong in regard to this, and they can sue you for your misuse or misapppropriation of their images--though $200/day may be an excessive amount, since what they can get is generally more-or-less related to the gain you received from using the photos, which for non-celebreties generally does not approach that level.The fact that they owed you money does not change the above--you still have no right to use their photos without permission. You do have the right to sue or countersue for the unpaid balance, and should do so if you are being hauled into court anyway.