I have been thinking about trying to do a trading assistant business as well. I live in an upscale rural/urban area and was surprised when I did a search that there are actually a large number of registered assistants in my area. I have not finished my research yet but think that you will have to consider doing some paid advertising such as mailers as well as using some contacts to try to spread the word. Look for local HOA's or business associations that will print your business card in their newsletters, advertising circulars etc. Tap some friend who work in large offices to let you sell their stuff and then they will have something to tell their coworkers about you.
Like I said, I have not started my consignment business yet because I am still in the research stage, but I am starting to network and hoping to have a business plan in the near future. Registering as a trading assistant on ebay will not get you there. You are going against the franchise stores who have nat'l name recognition, so you have to network your way into it.
Also, you need to have definitive fees and contracts to present to prospective clients. People do not want to see you as a startup, wishy washy, or worst of all negotiable. Make sure your ebay ME page is done, looks professional, describes your business, includes terms of service so people will be confident that you can handle their transaction.
This business is at least 50% research. Hope this will help you get started on yours.