As a host and a traveler, the reviews on AirBnB are complicated....not in how to post them, but in how it's easy to get good reviews if you want to do that, and how travelers have few ways to figure out if a review is really real, or not. Note: I no longer host as I've migrated by rental properties to long term lease properties instead of short-term stays.
One tip off to potential 'false positives', especially in foreign countries, is the first 5-10 reviews are in the hosts language - they've likely paid for those reviews or asked friends to review their place to give them good reviews out of the gate. When those reviews are then followed by reviews in a mix of languages and English, those are the ones to pay more attention to. With properties in the US, it's harder to tease out those first reviews because most of the reviews are in English.
That said, most places are good enough to please most travelers, so most reviews are likely more honest than not; part of that is also because travelers can provide feedback to the host privately (in addition to the public review seen by those considering a property) to let them know of issues they may want to take care of....many travelers are kind, so they'll use that option over publicly pointing out flaws in their stay, especially if they feel it's something the host can easily take care of, or something that was beyond the host's control.
Some properties are truly hideous though and what can happen is it'll get so many bad reviews, the host will remove it, wait a while, then relist it under a different company or host name. That happens way more than travelers realize, so they'll find a property that has no reviews and not realize that it is not going to be a good stay....AirBnB tries to prevent this, but it does happen and I know this because I actually wound up in one of the habitually relisted dogs in Avignon last year - three glowing reviews, in French, yet an absolute dump when I got there....it's a long story, but AirBnB did get us to a new property within 24 hours although we wound up having to stay in a hotel the first night of what we'd hoped would be an amazing stay in what we thought was an amazing looking property. To date, the property has not been relisted, it was removed and the address flagged to no longer be allowed listing on the site.
So far as contacting a host to ask questions - after the listing details, that first into description paragraph(s) on the left side of the page, there is a link (just text) to "contact host"....use that and you won't need to select dates, you'll go to the next page where you'll see their policies and basics and it'll have space for writing a quick note to the host to ask questions that may not have been answered in the listing; fill that out and click send. It is sent to the host with a different 'subject' line than when you send a 'request to book' or 'instant book' option that is to the right side of the page under the calendar on the listing.
One more thing - always check the reviews the host has in their profile - it's sometimes enlightening to see how they are as a guest or if they have more properties (and if they do, read those reviews too as it'll help put together a picture of their overall attention to their portfolio of properties or if they are simply a property manager in disguise as host/owner).....I've looked at properties and taken a pass on inquiry after reading the reviews in the host profile and found them to be difficult to deal with as a guest (one good thing on AirBnB is hosts get to review guests too) or if their other properties (or properties they manage) had reviews that were bad or consistently pointing out things the host could have and should have resolved.