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?
1. This is a letter from company like Facebook and my choice will never cause difficulties for them. I do not need millions of their reminders and my spam report in Gmail is being forgotten regularly.
2. This sender use to send me malware, for example some MS Word documents or doing something highly suspicious like distorting letters in a message obviously for breaking some spam filter.
I use to ignore all other spam messages, because I do not want to harm good people who use email for advertising.