Ask HN: What should concern a “guest poster”?

I've been asked to do some writing for a site, but I don't know who the person is doing the asking and his guidelines are rather amateurish. It really makes it sound like a fly-by-night operation, but then, many popular sites were originally started by naive go-getters who just kept cracking the pavement until it worked.

What sort of question would you be asking, what sort of things would you be looking for, to figure out whether or not becoming a contributing author or a guest poster on a new blog is worth the effort?

I mean, beyond just the time effort. Is there a potential to harm one's own reputation if one gets involved with a site that goes sideways? For example, there are lots of articles that talk about the best way to run a blog that accepts guest posts, how to avoid spammy content, how to avoid getting penalized on SEO, etc.