You don't need to worry about that. All the design contests are paid up-front i.e. contest holders have to make 100% payment upfront before launching a contest. then Designhill pays the winning designer.
If you’re selected as the winning designer, then please upload your final design files as soon as possible. Once the files are approved by the contest holder during the Design Handover stage, you will receive your prize money.
But if you are contacted privately by a contest holder, report it to Designhill immediately so we can take the appropriate steps. There is no reason for you to accept a payment that’s less than the listed prize. And never share your personal information to anyone on Designhill. If you are caught sharing, your account will be permanently banned and your profile will be taken down.