Im not sure I understand your question. For searchinbg keywords, I never use amazon nor ebay. Maybe, google keyword suggestions tool, wordze.com or even wordtracker.com Hope this help
You want to do keywords selections or research for your website ? If So use wordtracker and google adwords tools. or if not so please explain in details. Thanks John
If I want to sell a product, how I should do to find a good kw for index with Google and Yahoo. Please, help me.
install webceo and learn yourself. And keyword must be inside your website content else no effect in SERP. And also know that keyword is not from the mars but simple words like others' Example:- 'Good keywords' is the keyword for this thread as we have used lots of 'good keywords' in this thread.But it doesn't means that it is only one keyword for this thread.