Gentranum212 (second-hand image source)

Stumbled upon this "artist" just now (gentranum212). All their works are actually works created by other people that gentranum212 either commissioned or got permission to post.

I added the second-party source or third-party source tag to all images and moved 2 of them over to the correct artist but these were the only ones where they actually gave a link to the artist rather than just giving their name (which may not be the same name as danbooru has for them, or may even be a different person to whoever danbooru has under that name) or even saying they don't know who the original artist was.

What should be done with this?

Standard procedure in these instances is, at minimum, to ideally remove the tag and replace it with artist request; if need be, the tag (in this instance, gentranum212) may also receive a wiki indicating the fact that the art on their profile is not, in fact, theirs but rather what they have commissioned or received permission to upload (honestly, "receiving permission to post" I don't think I've seen yet for Pixiv, it's typically either commissioners or art thieves; here's two examples).