How do I skip importing a duplicate item?
I have a hard time parsing your question. This is what I think you want:


If the source item has a title that already exists on the website, don't import this item.
If the source item has a title that does not exist on the website, import as a new item.


So if above are your only requirements, it would imply that you don't need to update existing content. In this case, the solution is:


On the processor settings, set "Update existing" to "Do not update existing".
On the mapping page, only set "Title" as unique.


From your story though, I sense that there might be more going on than just the above scenario, but I'm not exactly sure what it is.