(I also suspect that some spammers may read this thread to get ideas as to how to make posts with a sufficiently large character count without having to write something coherent.
If spammers are doing this, I'm not quite sure what their goal is: if a manager is simply checking post quality by using the metric of raw character count, then it doesn't seem like a situation where you need to exercise this much discretion. You could probably get away with much more.
Managers may do a spot check of posts, but if you are creating posts with 100 characters instead of 150, and a manager has 30 participants to check that make 20 posts each, there is only so much scrutiny they can give to individual posts. Managers have to use some level of automation, and vet participants prior to allowing them to join.
Here is my makeshift spoiler, using the [abbr] tag:
█████Hopefully you appreciate this as a useful alternative. You just need the inner character, but it behaves functionally identically to [spoiler]
You are limited as to how much information you can keep in the "spoiler" as the display box will only be so wide.
Also, if someone is not sure what you are doing, they may spend an inordinate amount of time trying to figure out what is "behind" the text
"█████" without success, and never actually see the spoiler text.