One major barrier to finding work as a virtual assistant is overcoming the psyche of your potential client. Naturally, those that need a virtual assistant to outsource to are successful, busy and more than likely control oriented. So asking them to try outsourcing can be a daunting experience.
I've always used a free trial of some kind to get people to try virtual assistance. Usually this helps them reduce the stress of assigning me something and potentially having me screw it up (which never happens BTW). This seems to be the biggest fear amongst those that outsource. They realize that they will have to "train" me to manage their tasks.
However, despite whatever uniqueness a particular business might have, the tasks are almost always similar. This is key to helping someone overcome the resistance to trying a virtual assistant. Sharing success stories, testimonials or accolades that you have recieved will help your potential employers psyche and will make it less stressful for them to take the leap and partner with you.
I found a great article that shares one mans point of view on the same topic. Give it a read and see if it inspires you in some way: http://www.43folders.com/2007/09/25/enlightened-outsourcing-1
Have a great Tuesday everyone!