Turkey that has been pre-treated or pre-brined will be too salty. Large commercial poultry farms often add a salt brine to increase the weight and therefore the cost of the bird, "Kosher" turkeys are generally pre-treated with salt and aren't the best to use with a brine, as they will be too salty. "Natural" turkeys will most likely not be pre-treated with salt. If the label list "sodium" as an ingredient, it will likely be too salty to use with a brine. Look for a natural turkey or one that has never been exposed to salt