I really look at the letters from psych attendings from USMGs, and at the letters from a good US clinical psychiatry experience if I'm in doubt about an IMG. It's easy to fake interest on a personal statement, and not that hard to ace a SHELF exam, but I think it's pretty hard to fake genuine interest and enthusiasm over a 6 week clerkship or 4 week elective. Most psych attendings I know really like to recognize and cultivate psych interests in students who say they are interested, and they will not write glowing letters for students who show half-hearted interest.
In the interview I'm looking for some spontaneity and fluency in talking about psychiatric experience, maybe compare and contrast public policy issues in mental health between different regions of the US, or the difference between the practice of psychiatry in the US vs. India/Pakistan if that's where the applicant is from. Show me that you think about the issues, that they are a part of your life.
I like IMGs. We are fortunate to get the absolute cream of the crop--people who have worked d**ned hard to get here. That said, nothing raises the red flags more than someone with no US clinical experience, limited foreign psych experience, and lukewarm "generic" letters from psych attendings. Couple that with gushing about psych in romantic and glowing, but vague, terms and then having your first question about the program being "are you offering pre-match positions?" and I will expect that this is a resident who is not likely to be with us after year 1, if they do match at all.