You must set the price and then you will have to wait for someone to come and buy the fish off you...Then you will get the money...The cheaper the price the happier and quicker your people will come...
No one in particular.
Oil prices are not set by anyone in particular. Oil is traded on a wholesale market in big batches. People who wish to buy oil place bids on oil and are basically competing...
market conditions are responsible for price setting, as thing in perfect market are homogeneous, any different product with special feature would have a high price for it .