Practical 1 & 2
If I have $500 to spent ;-
these are the things that I would buy :-

Razer DeathAdder PC Gaming Mouse
Price:$108
~{-This mouse has an ergonomic right-hand design for optimum comfort while gaming, a fast response time of 1ms and a 3G infrared sensor that enables faster movement speed.-}~

Autographed AC Milan Jersey
Price:$122
~{-An autographed AC Milan jersey with signatures of Ronaldinho, Kaka, Shevchenko and Inzaghi. (They are soccer players if you are wondering)-}~

Phillips Keychain P44417S 0.1 Megapixel
Price:$25
~{-A 0.1 megapixel camera small enough to be a keychain.-}~

Coca Cola YoYo 1992 Shooting Star
Price:$14
~{-A limited edition YoYo by Coca Cola. A collectible item.-}~

Audio Technica ATH-M50 Headphones
Price:$110
~{-A headphones that offers maximum sound isolation, exceptional audio quality and collapsible design for easy storage.-}~

SpongeBob Plush Dolls
Price:$25
~{-A limited edition collectible spongebob plush dolls.-}~

Glance GB149 Swatch Watch
Price:$90
~{-A cool vintage Swatch watch.-}~

Doraemon Coin Purse
Price:$6
~{-A small and handy coin purse in the shape of Doraemon.-}~
Total Spent: $500.
Purpose of the website: I think the puspose of websites such as eBay and Yahoo auction is to provide a platform in which users from all over the world can buy and sell at lower price compared to the market. It allows the user to sell whatever items at any price. The fact that it is an online sites means that users can see what other people are selling from all over the world. It is also a place to find rare and exclusive items items such as limited edition watches to autographed T-Shirts. By putting up these websites, the companies are also teaching us the fundamentals of being an entrepreneur.
Difference And Similarity: The main difference I find in the different online bidding/shopping site is the items they sell. :P Sites like these have 1 thing in common; to provide web users from all around the world a platform to buy and sell things therefore, there will not be much difference among them. All of these sites allow the users to post the pictures of their item, price and description, allowing the buyer to survey what he or she wants to buy. The sites also allows bidding which allows buyer to get items at cheaper price or buying a rare item at higher price.