If you wanna buy any asset you can't directly tell owner, you need searching him in real life. I suggest develop bid system.
  • you finding needed asset;
  • if this asset selling on marketplace, you can buy it or send the bid, if not, you can only send bid.
  • you send bid volume and life time.
  • press "Create".
  • your ENJ blocking.
This method have some minuses:
  • enj bloked until bid expiration;
  • on each bid you spend gas.
Another way:
  • you choose asset, push the button " I wanna it".
[- send the price.]
  • each owner of this asset get notification on wallet.