Is this not a slightly selfish action? It solves the problem for you, but doesn't make the community better for everyone. I feel like blocking users should be reserved for issues like harassment, not spam.

This is an aspect that I had not considered. Even thinking about it now leaves me unsure of the best way forward.

Specifically, whilst it's a valid argument that blocking the user only solves this for me, and not blocking would help me see if the issue was dealt with, I feel that leaving the user free to roam across my screen is impacting me directly and if I'm not a moderator in a community, it's not my place to second guess their decision to leave such a user and post in place.

In other words, I'm stating to a moderator that I think that this post is spam and should be dealt with accordingly, but if you leave it alone, that's your choice.

I moderate several communities outside of the fediverse and spam in my communities is a one-strike ban. That's not what everyone does.

Having now thought through this again, now in more detail, I'm comfortable with blocking the user.