I started reading the page linked and I don't think the seller is even starting at the beginning for what you should do
1) decide what you want to sell
2) determine whether you can handle a low starting no reserve sale
3) find out consignment rates at various venues, payment schedules, methods of promotion etc
and that's for starters
4) do you want to sell them yourself on ebay?
5) is there actually value to selling your posters through someone else (how much are they worth, cost of shipping and other issues)
there are many other issues.