Got an idea for the marketplace. Why not remove the premium restriction, and instead add something like the Vapus Shop uses (where you upload the items your going to sell, and in order to download you have to pay to get access to that link ONCE), then instead OtLand could charge a SMALL fee (1-2$) in order to use their system. By doing so, OtLand admins would not only see that the content is legit, they would also prevent scammers/noobs to mass upload stuff.
When it comes to services they should be reviewed and vouched by mods before they are posted. For example my service where I pentest Otservers, I sold it and helped some mods on this forum and they could actually vouch for me that its legit. So in order for someone to create a for example scripting services, a mod should task him to create a certain thing, if he manages and can show it as proof that he made it, he should be allowed to keep it on the page.
If the trade is about an account or gold or such, an admin/mod should always be available as middleman.
Sounds like alot of work, but its just my opinion. If you gonna do something, dont make it half way, go all in