Can anyone enlighten me how the gold/silver etf earn money?

i quite unsure how the gold/silver etf can survive, if they don;t have the physical silver.
if the price go up, then where they get the money to pay the buyer?
but if the price go down, they can earn money if the buyer go out......

so if i am the etf owner, i will collect all the money from the buyer to short the gold price, then i can earn?

correct me if i am wrong.