It depends on the stage at which you refuse. If a client sends you an offer and you decline it before accepting, most platforms will not penalize you for that. But if you accept a contract and then cancel it early, that is usually where your account takes a hit. Some platforms track your cancellation rate and use it to lower your ranking or remove certain privileges. Have you ever turned down a job offer on a freelance platform, and did you notice any effect on your account afterward?