I have posted extensively over the years about using Ziebart rust protection on my vehicles. Beginning in approximately 1996, I have had every new vehicle we have purchased taken directly to Ziebart for rust proofing. Our area uses a lot of road salt and salt brine during the winter months and before I had them treated, our vehicles would be rusted through in just a few short years. Since I have been using the Ziebart product, we have not had (with one exception that I will explain in a moment) any issue with rust. Body and chassis of our vehicles look like new, even with many winters in the salt. The key to the Ziebart package I believe is the annual inspection/respray that they do. The annual inspection/respray is less than $50 and is required for the Ziebart warranty to remain in effect.
I posted a month or so ago that during the annual inspection, Ziebart found a small area of rust on my '07 above the left rear wheel. It is the first rust that has been on any of my vehicles in the nearly 20 years that I have been using their product. Ziebart is now paying for my truck to be fixed and then re-rusproofed when the repair is done. I am completely satisfied with the warranty claim process and the way they stand behind their product. I know the goal with rust protection is to not have a problem, but I am just amazed at their customer service and the way they have handled this issue.
I'm not sure how Ziebart handles used vehicles. I do know that they will treat them. But, I don't know what kind of warranty they offer in that case. Many here have also talked about another rust protection company that I believe is called Crown. We don't have one close and I am not familiar with their product. I would imagine that they operate similar.