I think our best option would be to making registration harder by including randomly generated questions related to the forum so they are both being taught how to use the forum as well as having to answer questions about it. These questions could be changed every 2 weeks or something to prevent bots learning how to answer them.
The idea makes some sense, but I think it would make registration quite difficult for some of the legitimate members. It should be noted that a large number of new members do not come from an English-speaking area, and that they would probably not understand the question/s - and would give up registration. It seems to me that this is not just about bots, but a lot of real people who have bad intentions and see in this forum an opportunity to achieve them.
Another option would be the shadow ban that has been talked about a lot. I think this would probably be the most effective way although again for this specific scammer attack they would learn to get approved by a staff member and then continue on their way of scamming but this would probably stop bots being able to easily exploit the forum.
I have to admit I had to look up what exactly it means shadow ban, and it is true what you say that there has been much discussion on the subject in the past. But taking into account the number of newly registered members (a year ago 20 000 new accounts per month based on this thread) some conclusion is that the staff/mods would have about 3000 posts per day to check on this basis alone, and to that should be added all the regular reports.
Yet the idea has potential, perhaps this post gives a better insight into how the whole thing might work.
