In the past we have run into booking requests where we would have liked to message or talk with the potential guest before hitting accept or decline. Where we have been able to contact guest in the majority of cases we have accepted them. The only time we have declined is where it became apparent that our listing would not be a good fit for their requested needs. We recently had a booking request but without any option to message until after we had accepted or declined. In that case we declined and were then able to message guest with reasons. In this case they wanted to be close to a specific area and we were fifty miles away. In my message I pointed out that and asked if they realized they would have a long commute. I also suggested that they look for listings in a town much closer, but if they really wanted to book here, we would accept them. They responded thanking me for the info and were glad I had pointed it out.
We therefore avoided having what might have been an unhappy guest. Airbnb lost nothing as they were going to follow my advice, but I believe that Airbnb will have a strike against us for a decline when it is their system that caused that by not allowing messaging first.