What are the benefits of web services to Amazon eBay and their developer partner?

I don't completely understand what you mean, but this is my guess. well if your asking The benefits, well, sometimes you find stuff cheaper. you don't have to get out and go buy it, you can also find older items that they don't make anymore. a downside though is the waiting time, sometimes you have to wait for a while, eBay sellers could rip you off too.