As stated in the EULA 2.2 Restricted Use, a participant, may not sell, lease, sublicense or otherwise transfer any rights to the Entropia Universe System to third parties. Which means that we do not support the selling of avatars, doing so will lead to an account suspension. Kind regards, Entropia Universe Support Source
And as not stated anywhere but as became publicly known through leaks this rule (and probably any rule) doesn't apply if you are a proud member of MindArk's buddy network.