You cannot stop a user from spamming, all you can do is report a spammers post to the moderator, though i don't think they are going to delete this members posts. My suggestion is to completely ignore this member and with time they will stop derailing this topic. I don't think creating a flag is appropriate for this, a trust feedback may be a better option, just to tell or warn other users about this member.
Both are on my ignore list but this spam has to stop and that is why If a flag is created I will support it. These two have been doing the blame game on literally every casino. You can check their post update and you will find them doing it. It seems they both are facing issues whenever they gamble on any casino.
Better for people to ignore every post they made since its clear that their intention is to create false accusation on each casino they go. Their post history tells everything so I think its not worth to spend some time to believe on their accusation and sentiments.
If people stop noticing their post in this thread for sure these people will stop especially if they know no one bother to pay attention on their crazy statements made.
There are other good things to discuss here and paying attention with those people creating fake allegation is just a waste of time.