So, you’ve found some vandalism or spam, and researched other edits by the same user account to see if there’s more. The next, and important, step is to post an appropriate warning on the editor’s user talk page.
The primary purpose of a warning about vandalism or spam, perhaps counter-intuitively, is not to get the problem editor to change her ways. (It would be nice if she did so, but troublemakers aren’t likely to reform themselves just because someone asked nicely.) Rather, when you and other editors post a series of increasingly strong warnings, you’re building a documented case for blocking a user account from further disruptive editing. If the warnings lead to a change of behavior of the editor before blocking is necessary, great—but don’t hold your breath.
Start by looking at the warnings that have already been posted on the user talk page, if any. Then take a look at the history tab for the user talk page: the editor might have deleted warnings by other editors.
There’s much confusion as to whether editors are allowed to remove warnings from their user talk pages. They are. Deletion is considered to be confirmation that the warnings have been read, and the warnings remain visible via the “history” tab. For details, see the “Removal of comments, warnings” section of the guideline Wikipedia:User page (shortcut: WP:USER). So you must check the user talk page’s history to see if prior warnings were deleted, but don’t revert ...