In US: To what extent does a collection agency filing by landlord affect my currently excellent credit score?

After I moved out last month, my apartment management is unfairly(in my opinion) asking me to pay $1200 for painting the apartment because of some crayon marks on the living room wall. I have always paid rent on time and have had no other issues with them. How will this affect my credit if I refuse to pay and they send it to collections? Thanks for input.