If you're running multiple studies in a short time frame, you can control how long participants have to wait before they are eligible for a new study. To control how long participants have to wait between being eligible for multiple in-product studies, you can use the Repeat study cooling period setting under Account > General.
For example, a Repeat study cooling period of 7 days means that no participants in your product will be shown a new study until 7 days has passed from the time they were shown the last study they participated in:
Use the identify method to exclude users across different browsers and devices
To ensure that participants don't re-enter a study even if they change browser or device, you need to identify the participant using the Wondering identify method.