eBay knows what you want.
You don't.
I understand what you mean by this, but it may be useful to look at this in a different way.
In a certain sense, eBay does not know what you want. At all. eBay only really knows what you are asking for.
The two may actually be very different things.
eBay may be able to infer what you want based on what you are asking for, and based on what others have asked for and eventually wound up looking at or buying. But if what you want diverges from what others have looked for previously, this sort of statistical inference may not be very useful for your particular case.
The better you understand how eBay works, and the better you understand and can describe what you really want, the more likely you will be able to ask in a way that enables eBay to show you results that you do want.
For very common things, it may be sufficient to use one or two appropriate keywords -- a brand name and a model, an author and a title -- and perhaps use a category or a filter to narrow to a particular set of results. For more complicated searches, where several kinds of things overlap in ways that are harder to distinguish, or where sellers may not use the same keywords to describe items consistently, more complex search techniques may be required.
