One of my answers got upvoted today on a question that has been closed as duplicate long ago, and after re-visiting it I've noticed the question body was edited to contain spammy text.
I've already rolled back the edit, however I'd like to know if there's anything else that should be done. Should I also flag the question for spam ?
I see three possibilities as to how that question ended up edited into spam:
While it might be interesting to know which of those possibilities it was, or perhaps some other possibility, for all of those circumstances the moderators should be informed about the situation. Thus, you should raise a custom moderator flag and explain the situation. The moderators can look into it with better tools than regular users have available. They also have the tools available to deal with the situation.
Alternately, you could have just raised a spam flag, but I wouldn't do that once you've made the choice that the original content should be kept on the site (i.e. once you rolled-back the edit). The spam and rude/abusive flags should really only be used for content which you feel should be removed from the site, and which is obviously spam, or rude/abusive. If situation requires explanation, additional context, or isn't obvious, then you're usually better off with a custom mod-flag and explaining in reasonable detail.
Basically, however, that question ended up as spam, the account should be dealt with in some manner (i.e. the account is currently controlled by a spammer; maybe it's originally their account; maybe the account's been compromised). Moderators are the ones able to deal with the situation. So, raising a custom mod-flag is the way to handle it.
The Charcoal team runs a bot called SmokeDetector, which scans all newly created or freshly edited posts on the Stack Exchange Network looking for spam and (some) rude/abusive posts. When SmokeDetector finds such a post, it reports the post into various chat rooms, with Charcoal HQ being the primary room for interaction with SmokeDetector or communication with Charcoal.
While SmokeDetector does a really good job of detecting spam, it's not perfect. In particular, it's significantly less adept at detecting spam in languages other than English. SmokeDetector, from time to time, doesn't detect some spam posts, such as the one you found. In Charcoal HQ, we're always happy to get reports of spam which SmokeDetector has missed. You can always drop into the chat room and say that you've found a spam post, or use the !!/scan <post URL> command to have SmokeDetector scan a specified post. From those reports, we generate additional detection criteria, so that similar new spam posts are detected.
From looking at the post you identified, I determined a keyword which I could use to search Stack Exchange for additional occurrences of similar spam. So far, I've found 3 additional, similar posts (1, 2, 3), all of which were edited into being spam. From those three plus your reported question, I created 13 additional patterns which SmokeDetector will use to detect similar spam. The detections could be even better if someone who speaks Vietnamese is willing to contribute patterns.
If you, or anyone else, is interested in helping out even more with Charcoal's fight against spam on Stack Exchange, we're always happy to have additional people participate. There's an Introduction to Participating.
If you suspect that something harmless-looking might be spam related, check whether it was plagiarized.
That question was copied from another question, and the user's profile text was copied from some random web page (https://ancu.me/thong-tin-thi-truong-bat-dong-san/danh-sach-cac-chua-dep-gan-sai-gon-cau-binh-an-dip-le.html).
(I've raised a custom moderator flag.)
