I suggest to have a personal in guild warehouse.. For example u put costume in guild, and ur guild member want to use it.. He/she can wear it, now the transaction is between u and the real owner.. U cant trade/sell the costume.. U can lose it if the owner retrieve it from the warehouse.. Just like the other item.. U cant amp, item from the warehouse as long as the owner of that item is still exist.. And if the member of the guild got kicked, his/her item will automatically bring back to the owner