The only way to get rid of that smell is to quickly re-paint the walls. Maybe not all the walls, but at least some of them. Use the same color paint and a roller to quickly paint over the walls. I would also notify the incoming guests that the room has been painted. Also put fans on the windows on full speed not only to quickly dry the walls but also to diffuse the smell.
We have had similar issues with odors in our house, it had been vacant before we bought it, and simply could not eliminate the odor even with painting the ceilings and walls. After trying so many different things with no success, we discovered an ozone generator works great!!! Got it on Amazon for 79 USD. “Enerzen Commercial Ozone Generator Industrial O3 Air Purifier Deodorizer Sterilizer, 6,000mg - Silver”.
Wishing you the best!