Hi Jerome,
Your advert is advertised as "multivendor" therefore is misleading, as it sounds like websites with this extension can Open for wider users to sell from your site. But from what you write here, no user can sell without being given a super-user rights, from the buyers point of view it is imbalanced from what you advertise as Hikamarket, you might know that people are interested in buying this extension especially because of being able to open his/her store as Multivendor, you know that from the questions raised by many buyers me included.
Although you intent to develop this extension further, it will be great for now to either develop the extension to accommodate this feature as soon as possible while you being absolutely clear to the buyers to be that Hikamarket does not allow different sellers to sell without being given the right of super-user and what exactly this means, or don't sell Hikamarket as multivendor.
Don't take it personally, I hope you understand the frustration this brings to many after they buy all of your extension to get to this stage and discover that.
S Cesar