@Susan1188 Airbnb doesn't provide any kind of useful guidelines to guests about what the star ratings signify, so the results are going to be extremely subjective, at times even random. There are guests who will dock you stars for all of the things you describe. There are some who will even demand a refund if they spot a hair. And there are also a great many who have some sense of perspective and rate you reasonably.
It's well worth aspiring to deliver your condos in the cleanest state you can, and take special care about sand. But you can't do anything to stop a guest for rating you poorly as a result of noticing their own sand, hair, etc.
Well...actually there is one thing you can do: screen your guests. In the initial communication, it's often very easy to spot the people who are going to be high-maintenance and persnickety and which ones are easygoing people who are genuinely appreciative of your home and hospitality. (Not naming any names, but you can also spot them in these forums). The former goes around the world acting all entitled, and won't hesitate to damage your business over a discolored towel; they often start their requests asking questions that a simple read of your listing could've answered, act vague about their intentions, and are likely to ask for extra services such as an early check-in. The latter guests show genuine enthusiasm and attention for your listing, express themselves in a genuinely personable way, and display enough flexibility to plan within your parameters.
The good-communicating guests tend to leave the best reviews. The entitled ones won't be satisfied with anything, and at worst even threaten you if they don't get discounts, or call the authorities to say you didn't have enough windows or whatever.
So yes, do your best to deliver a clean, presentable, sanitary property. But if you care about how your efforts will be reflected in the ratings, decline the guests from that undesirable second category.