Yes, it might be a problem, but it will all depend on the situation. If there is a reason that you have a bad credit score, that is genuinely out of your control, then they may say that they will allow it and choose to hire you anyway. If you are disorganised with your finances then they will not want to hire you because it means that you will lack certain traits that they will see to be necessary - police officers need to be completely on the ball, and if you can't be in your personal life then chances are you wouldn't be able to in your career either.