Due to the way that the API is set up in EveryAction, merging gifts in EveryAction will result in all gifts linked to a contact whose record has been merged showing in the contributions activity type.
In order to prevent adding gifts to the Raiser's Edge that have already been added, we recommend using the Contribution ID as the Raiser's Edge Gift ID. As the Raiser's Edge will not allow two gifts to have the same Gift ID, this will ensure that you cannot add the same EveryAction gift to the Raiser's Edge twice (you will see exceptions in the Control Report that indicate when a gift has matched to a gift already in the Raiser's Edge).
To ensure that the EveryAction Contribution ID does not match an existing Raiser's Edge Gift ID, we recommend using a Data Transformation to add a prefix to the number. You can watch a video walk through of this process here.
Please note that you should not change the prefix after you begin using this system or the contributions will no longer match and you may inadvertently duplicate gifts.