Spam posts usually occur on SE sites and main site is not an exception. Such posts should be flagged as spam and they do get flagged. However, what I have been noticing is that sometimes, they get edited and stick for long times on the site.
This has happened in the early days of public beta, and now it has happened again. I am not aware how many times such thing has happened during this period. However, this is not a good practice.
From this answer to the main meta post,
Spam doesn't usually stay there long enough for it to be cached by search engines or to have random users stumble upon it.
Most spams are posted to get a backlink from popular sites such as this one. But since spam is deleted before crawled by search engines, this will not happen.
From the same answer,
If a post is flagged after being edited, those flags will be invalidated if the post is rolled back; unless your edit actually results in a post that shouldn't be deleted, you're just creating an opportunity for someone to make the post stick around longer.
If the post is edited, the post will stick around little longer and the spammers will get their goal accomplished.
If a post is a spam, please don't edit it, flag it as a spam.