Precisely, the options are -
(1) Artists charge for their time at a pre-agreed rate.
(2) Artists produce art and let the market decide what it is worth.
(3) A panel of experts sit around determining the price of every piece of art ever made and it is illegal to transact at any other price.
Whilst I regard (2) as very unfair (it values my untrained and quickly knocked-up art as worthless trash, and Da Vinci as worth mega-money, despite the fact that it is clear to me that it should be the other way around), it is probably the best option.