1- A Scammer can open up a self mod thread about his service and would be able to delete all the negative feedbacks which people may wrote about his service.
2- A person may be willing to enforce his own point of view in one of his self moderated threads and delete the replies which differ from his opinion and thoughts. This may lead to the one-sided view on any particular instance/topic.
Besides that i don't think there are any more disadvantages to Self Moderation threads.
1, You are talking about the service section right but removing self-moderation feature from the service board is like double-edged sword. Imagine a service thread is actively undergo spam attack and the creator of the thread wants to keep the thread clean from spam which can reduces a lot of reporting work, moderation work. But I strongly suggest to remove the self moderation from
Marketplace where the option is only used to delete the actual words from victims.
2, Yeah but that is the point of self moderation and if everyone is against the content and OP keep deleting the words opposes it will no longer make replies so it will be buried into the pages. If I am not wrong in self moderated thread the creator can include his own rule too so if we don't agree with the content then simply choose to ignore it from engaging.