IMO, the best way to deal with these, if using gMail, is not marking them as spam. Instead, I drag them into the Promotions tab, answer "yes" to classify all emails from the subject as such, and that's it. Promotions == Trash.

I don't open/read such emails (I scan the first few words shown in the Inbox line, then dispense), so good luck trying to cold contact me for legitimate purposes.