Yes, a repo man can enter private property in Wisconsin to repossess a vehicle. They cannot enter a locked garage or closed space, or even unlatch a closed gate to do the repossession.
If a repo man enters your property improperly, they are trespassing. You can call the police to report the trespass. You may also be able to sue the repo man for damages.
It is important to note that even if a repo man has permission to enter your property, they must still follow the law. For example, they cannot use excessive force to repossess your vehicle, or breach the peace. If you believe that a repo man has violated your rights, you should speak with an attorney.
Attorney Nathan DeLadurantey offers free consultations to explain your legal rights in Wisconsin. Free consultations can be scheduled online.