Once you get the hang of it, it isn't hard to sell on eBay.
It is difficult to judge how much something for shipping, however, what I typically do is ship by USPS. I usually go to the post office when it is closed and weigh the item on the scale. Then you can calculate the shipping cost (approx). I always indicate that insurance is recommended. I am fortunate that I am usually pretty right on with the shipping cost.
Some sellers give a flat shipping price and that includes a "handling" fee, similar to if you bought an item from a store. They inflate the price to inflate their profit.
One thing to remember is that you need to factor in the fees that eBay charges you to list the items as well as any fees that you would be charged for using a service like PayPal. Those fees should be factored into your starting price so that you aren't losing some of your profit. The fees are small, but if you are selling items for only a few dollars, that will eat away a large % of your profit.
Here's an idea for those that are willing to put some cash out to get more back. A woman that I met at the hair salon was telling me that she actually eBays so frequently that it has become a parttime job. She has a credit card that she uses solely for eBaying. Here's what she does. She goes to the popular children's stores (Children's Place, Limited 2, Gap, Gymboree, etc) and goes immediately to the clearance rack. She does not look for things for her kids (that's what I do! ). She then looks for anything that will be priced under $5 when the discounts are removed. She doesn't matter the size of the clothing, just that it isn't ripped, is still in style, etc. She doesn't care what season the clothing will be worn in. She pays for the purchase with her eBaying credit card. Goes home, cuts the price part from the pricetag, which would leave on all the SKU/color identifiers. She then lists the item on eBay at a starting price of a 50% markup. So if she bought the item at $5.00, she lists is at $7.50. She gives it a 7 day auction, and if it doesn't sell on the day after the auction ends, she takes it back to the store. I asked her how much time/effort goes into it and she said that she really loves shopping so it is fun to go shopping for things that she isn't going to have to pay for in the longrun. She typically spends up to 5 hours a week shopping and then listing the items on eBay. Then about 1 hour to package/ship the items. But she makes in upwards of $100 profit a week. In theory, you can take this idea to any store and be able to turn a profit. Just watch which stores do not allow returns on discounted merchandise. A few other suggestions for stores/items to shop are: toys, books, video games, bathing suits! (very hard to find after the season - I know from experience because I forgot to get a bathing suit for our trip to Disney in December and it was like pulling teeth. Ended up having to pay $45 for a toddler's bathing suit from Blizzard Beach).
If you have any questions about eBay selling, I will try my best to answer them for you. I am by no means a pro at it, but have bought/sold over 100 items.
Some great items to buy from eBay~
www.restaurant.com (click on eBay icon at bottom of page, lets you bid on restaurant gift certificates), inkjet ink cartridges (typically get my cartridge for less than $20 - in store is costs $30), Disney snowglobes (any collectors out there?), toys.
Good luck to all! Sorry this post is so long.
) but he set a dollar amount and said as soon as I hit that amount then we'd talk seriously about a trip. 
Beleive me when I say It couldn't of been easier to list.. Good Luck and Let us know how you Do
