In case of doubt and when close-voting doesn’t seem to be the appropriate action for you, simply flag each post individually.
The usual way to handle things would be:
- Check if you can enhance the post with an edit, to make it (more) on-topic.
1. fails or doesn’t make sense, close-vote and choose the according reason. If none of the predefined reasons fit, you can choose to add your own – which will be added to the post as a comment so people know the reason for your close-vote so that they can agree if applicable. Of course, this 2nd point only works if you have accumulated enough reputation to cast a close-vote. If you haven’t, jump to
3. while skipping this 2nd point.
- If you think
2. doesn’t seem to be the appropriate action or if you lack the reputation to cast a close-vote, flag the post so that (one or more) moderators can take a look at things and – if needed – take appropriate action.
On a side-note: I would not really call re-posts “spam” in each and every case. It’s not uncommon for questions to be reposted every now and then… even by different users. Sometimes that can turn out to be a good thing since some users are able to choose a better formulation which is able to pull a specific question into the on-topic area.
In all other cases (especially copy-and-paste reposts) things will tend to get close-voted and/or flagged for the same reasons as before, mostly resulting in the same closure as before. It may be a bit annoying to “repeat the loop” in these cases… but there’s not much we can do about it.
If you can’t enhance things by editing it and if a question can’t be saved from being off-topic, so be it. In the end, that’s what the close-vote and flag buttons are for: to safeguard the quality of Crypto.SE.
Don’t be reluctant to close-vote and/or flag something if you think it makes sense. Doing so, you’re giving a heads-up to other community members about a potential issue. If enough users (or – if applicable – a moderator) agree with your close-vote or flag, the related post (Q or A) will be closed. In the unlikely case you happen to close-vote or flag something for the wrong reasons, no one will agree and you and things will remain “as-is”.
Besides: you can trust in the fact that we moderators keep an eye on things too… sometimes coming to the rescue by reopening and/or undeleting things when something got flagged or closed too quickly or for the wrong reasons. In our endeavour, we tend to like flags as they tip us on our back, telling us that we need to take a look at a potential issue we might not be aware of yet. So, flags help moderators to notice things that may need their attention.
Long story short: you can hardly mess things up by sharing your opinion with a close-vote or flag – as long as there’s a good reason for doing so. If something is really wrong with a post, pushing the flag-button is the most logic thing to do. In less problematic cases and assuming you have gained the reputation to do so, simply drop a close-vote with the appropriate reason.
Hope that helps…