I had a prospective agent check my Amazon listing once, only to find no books there. She turned around and told me I'd lied. Well, I didn't. As it happens, there are other countries in the world people publish books in. Like Australia! Needless to say, I went with another agent.
Amazingly enough books published in Australia, and even really foreign places...like yanno..Kansas, turn up on Google. If you've been published and you want to acquaint an agent with that fact you need to mention the title, and the publisher( the year published is helpful too).
If you don't, and we can't find it, I'm sorry, but we assume the worst. And it's not cause we're such raging curmudgeons, it's cause there are more people who think vanity press publishers are legitimate credentials, than are querying American agents with Australian books on their resume.