If Apple cider vinegar does not work to remove a stain, what is a the best slightly more aggressive treatment that will not damage the floor?

Hello and thanks for your inquiry. We recommend using a dry mop or vacuum (without a beater bar) to remove any dirt or grit. Then clean the floor with a damp microfiber mop, using a suitable diluted vinyl floor cleaning solution (neutral pH). Do not use dust mops treated with oils or silicones, acetone, strong alkaline cleaning agents, multi- surface cleaners, vinegar/ammonia/ citrus oil solutions, scouring powder, strong solvents, or abrasive cleaning pads, as these can damage the floors and void the manufacturer's warranty. Hope this helps. Thanks again.