I received an unsolicited email from a webshop I used once a year ago: "Write a review and get a discount!".
There was no link to unsubscribe from these emails and seemingly no way to contact them (the email was sent from a no-reply address, etc).
So I wrote a very short and to-the-point review: "stop sending me spam".
...and got a 5% discount.
For people who care about, support, or build Free, Libre, and Open Source Software (FLOSS).