I don't think he was trying to put you down, I really think he was just letting you know that we need more information to help you further.
As for the sorting of your downloads folder, you can open it up in Finder and then go to the column of Type, and click on the column header. This will group the files by Type for you. So all PDFs will be together, all .dmg (usually and application image file) will be together and so on.
It still doesn't alleviate having to preview each PDF, but it will at least separate them out from the other filetypes and possibly help you avoid deleting something by accident.
Also, when you empty your trash, if the system doesn't ask if you are sure, then you can turn this on by making sure Finder is the active application, then going into Preferences under the Finder menu header. There are several other toggle based options for Finder in there as well that I've found quite helpful to me.
Hope this helps, and seriously, I really don't think he was trying to put you down at all.
Best,
Brian