A while ago I have received an email asking to sign-up to a startup and feedback if I won't do it. I have got 3 automated emails like that, and I said - OK, the emails are well crafted, I might give them a bit of feedback despite my limited time. I spent ~30 minutes checking their offer, content and writing a long email. I have highlighted what I like, what could be improved and no bs reason why I will not sign up at this time (nothing offensive - their pricing is "off" for me). I have been very honest with them as we all know honest feedback goes the extra mile.
I have never received a reply, no thanks, no nothing.
This raises all kind of red flags for me.
This should be one of the core rules of a founder - always respond to feedback emails!