We faced a problem with our Lordmancer II Slack channel. There were many scam messages every day: in private, in general channels, etc. We constantly banned those spammers, but they just registered once again (even the names were the same!). Also each day we saw new members with names like "CEO", "cofounder", etc.
Finally we dicided to close the Slack channel. Now we use Telegram group
https://t.me/lm2ico as a main communication channel.
I strongly recommend not to use Slack for ICO campaigns!
Used the Slack it or not, participants must know that there are obvious scams. It was part of the money making system now and never it will gone. Not just in Slack but almost every platform where lots of people are engaging.
What users must do is to used their working mind and knows the obvious one. Since they engaged in ICO campaign, Im sure majority of it does have an idea about obvious shit like phishing attempt or any kind of fraudulent activites.