I can't tell you if you have a legal action worth pursuing but I think the slogan is just iffy enough that a review by an attorney in your area could be smart - this especially if you know other salt scrub sellers selling genuine salt scrubs who are equally concerned by the advertising slogan. The slogan appears to me to convey a false impression which can be corrected easily with the elimination of the word "the."
That said, you have heard from many in this forum who disagree with my assessment and who believe it is better for you and your wife to devote all energy and money to your business and marketing of your product and ignore what The Keys Salt Scrub is doing to market its product. But you could always conduct your own limited consumer survey to see how consumers interpret the slogan. And it is ultimately up to you whether you want to go to the expense of seeing a Florida attorney for a personal review and professional opinion.
Good luck. Next time I am in Florida, I will have to try out a salt scrub.