There's positives and negatives to self-modding threads. Self-modding is a good tool to keep trolls and shady competitors out of your business, but these days it's mostly being abused by scammers, sadly. With that being said, users locking threads are usually huge red flags of scammers and tell me who I need to stay away from.
I think we should probably consider restricting who can actually self-mod threads though and removing this feature from lower ranks would help. As I mentioned in another thread on the same topic, we should also maybe consider that once somebody locks a topic in the marketplace it cannot be unlocked by anyone other than staff because locking a thread to prevent warnings from even being posted is also being utilised by these scammers and is another huge red flag.
Suggestion
Only members and above can make Self-moderation topics
I think this is a viable solution. Generally speaking, higher ranked members who use self-moderation use it for legitimate reasons. Perhaps self-moderation could be another perk of Copper membership for new members? Those who have invested a non-trivial amount of money into their accounts probably won't abuse it either.