There are a number of things that can cause/make this worse. The clamping action on some tire changers is one. Most machines have protective boots to prevent this but many shops don't take the time to use them. Another possibility is where the inside wheel weight clips to the rim. The attaching/removal of the weights chip the chrome slightly and corrosion starts. All this adds to your problem. Road salt accelerates the process. Once you have the rim cleaned as best you can, they do make a rim sealer that works pretty well. It has the consistency of thick black paint. It should be applied either to the rim or tire bead before tire mounting. Any place that does tire work should have some. Hope this helps.