search(+A +B) and search(+A -C)

Anymore it seems impossible to do a Web search that includes particular terms. A search like

"+A +B"

gives results where term B is not in the search results. Google does this, and now DuckDuckGo does it too, and as far as I can tell, so does Bing. And if you try to exclude term C

"+A -C"

the search results still include C, especially, I think, if it's commonly associated with A.

Does anyone have a solution for this? I think it's because the search engines don't want to return null results because they want to include their advertising links. 

It's frustrating. Or am I doing something wrong?