If a customer is asking totally new, unrelated questions on a question thread that has been answered, then you can politely let them know that the site requires a new question page for new, unrelated questions, and they can request you if they wish.
Customers can ask follow-up questions related to and triggered by the original, and that should be on the same page, not a new page. That doesn't mean they should drag it out for days or weeks. You can use the Additional Services offer for More Q&A Time, but it still should be about the original issue or related follow-ups.
If a customer is having questions regarding the site policies or they are having any site related issues, they need Customer Service assistance. You can give them this link: http://ww2.justanswer.com/help where they can chat, call, or send a support request. Or they can email directly to firstname.lastname@example.org
Just let them know that you're a site user like them, but that JustAnswer Customer Service will be happy to assist them.
If you prefer, you can use the customer report to alert Customer Service department with a request to assist the customer.