Not quite instantly. Not just by smelling them. But you can judge them the way you size up someone you meet at a party. If there's chemistry, you know right away. You get tricked by a trendy haircut or a dazzling smile.
Some people take a long time to get to know.
Some people may be noble, honest, hardworking, decent, whatever, but not your type. What you want in a manuscript, in any case, is not something that's just nice, not something merely competent, but something that makes you gasp. In the first screening I look for a reason to stop reading. But it's easy to make mistakes. And I get tired.