Would questions regarding how to deal with customers be acceptable? The FAQ is sort of vague in this regard...
This is not an official answer, by any means.
My opinion is that it is like anything else that can have in-context and out-of-context relationships to the workplace.
Certainly your relationship and interactions with your boss are on topic. However, there are absolutely components of your relationship with your boss that are very job-specific; and those would probably be off topic.
I think the same would go for customer relationships. How you might acquire them, when your role in the sales/service process dictates that you should or shouldn't contact them — these things would be off topic.
But, just as we have many workplace relationship questions here, there are certain aspects of "how to deal with customers" that would definitely be on topic. Here are some samples that might be:
I believe questions like this are every bit as on-topic as other workplace relationship questions we already support, so in answer to "would questions regarding how to deal with customers be acceptable?" I don't think there is one answer that fits all questions.