The differences between eBay and Yahoo are numerous. The most important difference can be characterized by saying that Yahoo is a Seller's site and eBay is a Buyer's site. Most of that has to do with protection and accountability. Both sites are worlds apart when it comes with dealing with Buyers and Sellers and is, in my opinion, the biggest reason why the sites will not be able to have any kind of significant partnership in the future. In the end it all comes down to a Japanese person's willingness to do international transactions, and that won't be changing anytime soon.
Yahoo: Sellers have all the Power
Sellers are king on Yahoo. Their position is mostly due to the fact that payments in Japan are done via bank transfers, and once you transfer the money into the Seller's bank account, there's no way of getting it back. There is no middle man. There is no claims process. There are no holds. You've literally handed your cash over to him and getting it back cannot be done unless he actually hands it right back to you. Paypal exists in Japan but no one uses it because they already have an established transfer method that safer, faster, and cheaper. PayPal will never be able to overcome those obstacles.
If you do happen to get an item where you're not satisfied your sole remedy is to ask the Seller to give you your money back. And it's completely up to him if he wants to or not. And most of the time they will not. Why? Because they don't have to.
In addition to controlling the money, Sellers also have the right to cancel the transaction after it ends. They don't need your permission, they just need to click on a few links. Not only is the transaction canceled, but the Buyer automatically receives negative feedback for the transaction. Not only is it negative, it's a special negative that puts a nice red bar over the feedback so it really stands out.
In short, you can win an auction and pay, and you could receive nothing and get negative feedback and not be able to do anything about it short of filing a police report. Good luck with that.
Sellers also aren't nearly as restricted in terms of the types of items they can sell. Yahoo has a newly formed reporting process but it's mostly a useless affair. Sellers routinely sell illegal items with little to no impunity.
eBay: Buyers have all the Power
Ebay knows they're big. And they know they're famous. They know Sellers will come since it's the best option for them to sell their items. Over the last few years the powers-that-be have recognized this and have created a marketplace where Buyers have complete control. Buyers have multiple claims processes that just don't exist on Yahoo. The new system even guarantees that they cannot even receive negative feedback. Even for the smallest reason any Buyer can make a claim and put payment on hold to the Seller, or they can just call their credit card company and reverse the charges if the want to bypass eBay and PayPal altogether. Buyers are free to leave negative feedback whereas Sellers cannot even mention poor performace from a Buyer, and auctions can be pulled with little to no evidence of wrongdoing just by having a Buyer click on a link.
The entire system is set up to entice Buyers to come. eBay knows that a Buyer can go to Amazon or another website to buy, but it's not so easy for Sellers to switch over to a different website. And for auctions, there is no different website. Sellers will come just because eBay is eBay, so eBay is changing their focus to make the site more Buyer friendly.
Conclusion
Because of the differences in payment, protection, and ratings, the two auction systems are exact opposites, in my opinion. If you're an eBay user switching over to Yahoo you need to understand this. And if you're using a proxy service or buying from overseas it's especially important that you understand this. Once you send your money there is nothing else you can do besides leave negative feedack, and if you're using a deputy service you most likely can't even do that.
