Well this isn't what you're talking about but I consistently have the feeling that I'm faking it.
Yes, this. But, rather than cry most of the time, mine will sometimes give me body memories.
If I have somehow faked it without knowing it, then I have also fooled a T who has heavily researched DID, and worked with both DID clients and spouses before. When I say that sort of thing to my T, he says, "Because, obviously, you're having so much fun?" Or he will say that at best, even if these parts were slightly less dissociated (although that's not his opinion), there is no way they don't exist and I'm lying about all these thoughts and feelings being inside.
Basically, I agree with the others. If one were to fake it, it would be an awful lot of work with minimal to no reward. If you're out for sympathy or attention of some sort, there are far easier things to fake, I would think. If I had to consciously keep straight all of my parts' "stuff" every time I talk to T or H or others with whom I regular discuss it, it would be like a full-time job. Also, sometimes their stuff doesn't quite make sense to me at first, so if I were making it up, I'd probably make it all logical, as I like it when things make sense. Otherwise, I'm scared of being invalidated.
Well, I guess those are more reasons I know cognitively that I'm not faking it, despite often feeling I am. But, not knowing if this person you're talking about is even diagnosed, I can't imagine they would fake whatever symptoms they are describing to you. If they were, it would become a lot of work really quickly and that would get boring, not worth the effort. They couldn't keep it up.
I can't really recommend too many resources. I read a lot at first, last May, but I have to avoid reading too much now, because I will relate to things ("That is just what I have experienced since my teens!") and have an immediate denial reaction from a particular part in response. Or I will read on forums (this and another one), other people saying it is supposed to manifest exactly this or that way, treated exactly this or that way, and what does and does not qualify as DID and I get so much invalidation from a particular part and it sends me into crisis with the parts, because we are basically calling their wounds a lie or telling them they are being bad/wrong by their time with T not being what others say it should be.