In my opinion, if a spammer is a disease then negative trust is the cure until they are fully aware and recovering from the disease. I have seen DT members send negative trust to spammers on my local board, but what about spammers on other boards especially the 3 boards that you mentioned on the OP ?
Disagree. The trust system shouldn't be used to tag spammers. Spamming is against the rules, and these users should have their posts deleted or accounts banned. Being a spammer doesn't inherently make one untrustworthy. Negative trust also doesn't matter to the majority of spammers. Most bounty campaigns which pay them in their worthless tokens don't care about negative trust. What does matter is having their posts deleted because then they don't get paid for them. I would encourage everyone who frequents these boards to report spam posts rather than just skipping over them.