i get your point but i will list out possibilities one by one
1.Making prontera lively with the help of vendors: A big no no.WHY?? People before playing any server wants to know whats the population.Imagine when they see that eir has 100 people online only to find out 70% of them are vendors and rest of them are either afk or dual clients.Its like mitigating a false propaganda and is like cheating newbies.Slowly they realise the truth and leave server.Whatever players you gain is short term and not long term.
2.Why quality of shops go down: Lets be honest most of us sell junks from MvP loots or items gained while leeching.They are in excess and literally everyone sells them.they are under priced but whats the use, most of them are meant to be used by trans classes (like 70% of them)
3.We have trade channel through which newbies can immediately ask for buying or selling equips and can actually know its base value without being cheated.Yes it helps them a lot and this way we can keep in check OP stuffs that no one buys.Nobody can dedicate there timely hours for countless farming(if they can,well good for them)
4.We can also have B> and S>subforums. Not only they will have latest info on the server status but also can keep a track from there work place when they cannot be online.