There is no way to officially block someone on Glip right now-- you can open a case and explain the situation, and the spamming user may be able to be banned for violation of Terms of Service by the Support team.
USA-based acct | 2287 Users | 3800 DID lines | 28 sites | all Polycom VVX500 phone handsets
Not being able to Block a user on Glip is a huge shortfall - every other chat platform has that ability. Expecting to rely on compliance with TOS to remediate this issue is not a valid solution.
Please forward this thread to engineering team. If they want to compete with Google chat, Skype, Slack to name a few - they have to upgrade the product to Enterprise usability.
Because we need Enterprise-level administrative and security features including virus scanning of attachments, moderation of chat messages sent to groups, we have completely restricted the use of Glip on our network.