You may have noticed in the new source games that there is this 'Lerp' stat in the new net_graph command. While you may not know what this is, it's very important to keep it at a constant number, and make sure that it never turns orange.
This 'Lerp' stat is basically the hitbox delay between you, the server, and other other players, having this balanced out or synched with the server is very important.
Many people might complain about the hitboxes in DOD being to small, or too big, or the registry sucks; but for the most part it's totally client side usually having to do with incorrect default commands that you must fix yourself.
If you're one of these people suffering from your shots not registering on servers, there are a few commands that can solve this quite well. I've play tested these myself and seen a vast improvement.
^^ Tested on Listen server and lowered ping from 20ms to 0-2ms.
If that folder doesn't have an autoexec.cfg file in it already, create your own by opening notepad, paste the commands above in the file, and save the file as 'autoexec.cfg'.