Hello CH! In order to prevent the continued duplication of other designer's submissions, I suggest you #guaranteed your contest. In that way, you can see the submission of original ideas and use this following links to have an idea of what is a generic prefab logo: (beware! Because you might get something similar to these as well, happens almost every time)
Now you can be sure which designer is giving you a design completely made by itself and you can feedback and rating to guide them get better. Some of the designers feel more confidence to participate in contests that offer to protect them work by guaranteeing the final price.