http://pages.ebay.ca/help/sell/fees.html
Very generally speaking, you will pay about 20% or a little less of your customer's total payment in various fees.
Since some fees have a minimum on very low selling prices you may end up paying more in fees than you sell for.
Don't ever list an auction item to start at 99 cents as eBay stupidly suggests.
Always work out the shipping cost to a few different postal codes when setting your asking price. Buyers hate spending more on shipping than on the actual item.
And consider using Free Shipping, which just means including the cost of shipping in the asking price.
Which is cheapest:
A $5 item with $10 shipping
A $10 item with $5 shipping
A $15 item with Free Shipping?