A dirty restroom tells me that the management really doesn't care about my health or safety. It is fine with them if the germs crawling around on their dirty facilities enter my body.
Yesterday my husband and I entered a new store in an old building. It was bright, well lit, well decorated, organized, and appealing. I went to the restroom and was shocked at the condition. The outer portion of the sink was white, but the inside was gray. The toilet was not filthy, but needed cleaning. As I walked back into the store to meet my husband, I saw a poster that said, "Your Experience Here Matters To Us." I thought, baloney. If my experience was important to you, you'd clean your bathroom.
If I were manager of a store, the restroom would be clean if I had to clean it myself. There are products that will clean the stains out of any porcelain sink. If nothing cleans the sink in a business then try this. Buy A New One. But give your customers as clean a restroom as the store your give them.