[snip]
Self moderated topic is a must in there.
Well you already answered your concern --a self-moderated thread is essential if you don't want irrelevant answers and locking the thread is a good action if you have been satisfied with their response.
For me --it is a discussion board and as long as it discusses relevant to your questions does not matter if the response did not help your question directly. People are free to give their opinions as long as it is related to your question and that board called
[gambling discussion] to discuss their opinion.
However, if there is an off-topic reply or response, just hit the button
[Report to moderator] and the moderator will surely delete their reply.
It's cocky to say that in the Meta section. I think you should read the forum rules again. Especially the first one, because before the off-topic rule there is another one before :
1. No zero or low value, pointless or uninteresting posts or threads.
And it's not up to readers and moderators to report and delete spams, it's up to posters to follow the rules and to refrain from spamming first. It's the same thing as a thief telling you I'm free to rob you because if you disagree you can call the police...