"Sometimes these matches do have ancestry trees that are not linked to the dna test. You can look at these for clues."
If you're referring to your matches that don't have a tree attached then yes you can see them but you may as well be looking at any tree on Ancestry that shares surnames since without the DNA being attached to someone in the tree there's no way to tell who the DNA match's direct ancestors are. I suspect Ancestry defaults to the home person in the tree for the calculation and that's probably accurate a lot of the time but I'm not going to waste time and effort on a tree when I can't say for sure that the owner is even the correct starting point.
If you're referring to private trees as your post implies you're just plain wrong.
FWIW: The private tree matches I receive are going to continue to go to the trashcan until Ancestry provides me with some sort of clue as to the who, what, or where of the DNA match. I may be missing a clue or two by doing that but my experience with private trees so far tells me that the odds are long and the messaging hassle is more effort than it's worth.
The above said, my thanks to the few private trees that I reached out to early on who gave access without the plethora of excuses. They were the exception to the norm.