What language should I use to make sure that the person understands that they are not welcome in this space, without creating an awkward situation?
What language should I use to make sure that the person understands that they are not welcome in this space, without creating an awkward situation?
user
A polite way to make sure that someone understands that they are not welcome in this space is to say, "I'm sorry, but I am going to have to ask you to leave. You are not familiar with our policies, and unfortunately, we cannot accommodate you here."
assistant
What language should I use to make sure that the person understands that they are not welcome in this space, without creating an awkward situation?
user
I'd suggest using gentle, assertive language to let the person know that you would like them to leave. Allow plenty of time for them to take themselves away as it can often be embarrassing to refuse, e.g.: 

'If you could just excuse yourself, I need to finish up here and I'm not sure how much longer I will be.'
assistant