[phs318u]

Ban them? You haven't said but I assume the vendor's presence in the Slack is not disguised. Either way, it's your Slack and you're entitled to determine who is welcome and who isn't. You are under no obligation to be providing your competitors with a free channel and free leads.

[nduncan_hmc]

Their presence is disguised. They're creating accounts using gmail addresses and fake names. Edited my post to make that clear.

[phs318u]

Make a big deal about the shill/fake accounts. Educate people as to the benefits of your offering vs theirs and explain how even with their "free credits" offer, it's a poor alternative. I presume these offers are made in DM's? I'm not aware of any "forum" type software that allows admins to prohibit DM's.

[nduncan_hmc]

They're actually googling people's names, seeing where they work, deducing their work email, and emailing them.

Looks slightly less shady than DMing them I guess.