Ask HN: Ethical issues marking email as spam?

I recently got an email from an "experience management company", on behalf of a local plumber whom I had recently hired, asking me to rate them from 0 to 10. After I deleted it, I later got a "reminder".

I find these surveys annoying, and I never gave the plumber permission to give my email address to third parties. If they want my opinion, I would be happy to actually talk to an employee of the plumbing company. My impression is that outsourcing this kind of thing correlates with poor service, and indeed I was unhappy with the plumber.

If I understand correctly, marking these messages as spam in Gmail might cause difficulties for the sender (i.e. the survey company, not the plumber), leading to more of their messages to others being routed to spam. I view this as a positive outcome. However, I know that HN readers have been on the other side of this story.

Should I think twice before hitting the "spam" button?