Sending unwanted/unasked for DM's and emails, especially to multiple people. If you'd like to DM or email someone, ask them first. If someone has sent you an unwanted DM or email, get in touch with an administrator and we'll look into it.
Spamming channels with offers/invites to your service. You're welcome to talk about what you do if it fits the conversation that's happening in the channel. If someone asks you for more info, it's cool to share details about your service with them.