It does say on the website when they are trying to get you to turn on IB that one of the benefits is that you can cancel penalty free if you do not feel comfortable or the guests breaks your house rules. It says it twice. It does not mention a limit on how many times. I used to see the 3x allowance. There is probbably invisible fine print there.
I have had Airbnb cancel for me three times, no penalties.
1. Girl used IB and then asked if she could have an extra person even though she saw that it says MAXIMUM TWO GUESTS. I told her this was not possible. They were coming for a music festival. I called Airbnb and asked them to help her bug off. They did. I turned off IB.
2. I had IB turned back on but this guest did an inquiry first. He booked but then a few days before his trip I got pnuemonia (actually had it for months but I am tough) and I did not have the energy to deal with a guest and did not want them getting sick. I asked the guest if they wanted to cancel and they said yes. Because the trip was in 24hrs I called Airbnb and they canceled for me. I even got a message later asking me how I was feeling and they hoped I felt better sooner.
3. I had a young man IB for 2 weeks using his sisters account. I told him third party bookings were not allowed and that he needed to register himself. I contacted Airbnb and explained to them what happened. They read my explanations to him and they canceled his booking with no penalties to him and he booked himself a half hour later. One of the best guest I have ever had. He stayed an extra week.
I think a lot of it is situational depending on your hosting history, the guest, reasons, conversation thread, the customer rep you get, the phases of the moon and if Venus is in retograde. There should be a highly detailed policy that is uniformly adhereed to while acknowledging that sometimes things happen outside the normal parameters.
I had three people cancel on me. One canceled due to change of international travel plans. A host canceled 20 minutes after booking because he had not read that it was a private room and he wanted a whole house to admittedly party. He also asked me what the moderate cancellation policy was. The last cancelled within 10 minutes of booking and I have no idea why. All were well before the travel dates.