Sorry for miss understand here. I mean donate feature to buy bonus from the website. I think this is one of reason who have money can buy alot of bonus, so they can get/buy best items from lottery or buy other players and get stronger quicker than other. Without buying bonus feature, players will have the same change to grow up in game.
About the issue of Group like you mentioned above to sell stuffs for real money. I see this problem on most of Game. I'm in Viet Nam too so I know much of people here do that to make some money, however in some case that make the game more interesting and crowded, just find a way to keep that little as posible.
But i don't think that make the item price droping, Buying bonus make total bonus in game bigger quickly that make the bonus value down then also make the item price down. Shoul;d have another way to get bonus like Boss Hunting or Doing Quest and keep total bonus in game grow up in a managed way. Like Bitcoin, total new bitcoin value added each day is limited that keep it's value grow