What the difference between art gallery owner, art collector and art critic

The art gallery owner well, buys the paintings and then sells the paintings off to the highest bidder/the person who buys it for the set price. The art collect is a lot like the gallery owner except they buy paintings without the intent of selling them off. The art critic does neither buy or sell. But they can usually sway public opinion of a certain piece and make the gallery owner sell it for a higher or lower price than they initially were going to sell it for.