This probably goes without saying, but, if the buyer decides to cancel, attempt to resolve the issue (within reason). Even if your service turns out to be something different than they first thought, offer an alternative. I’ve been able to keep, at least, half of the cancellations from going through, because, we reached a satisfactory agreement. If, you can’t come up with a solution, then, keep your good humor & say that you hope you’ll be able to work with them in the future. It’s not always easy to maintain a pleasant disposition (and some buyers may turn out to not be worth retaining), but, it can go a long way in increasing repeat business & possibly having them recommend you.
Great advice! I recently had to deal with this.