Yes it is. And yes, it is. Two domain names have sold recently for very large sums of money. The asking price for some domain names has been reaching out of this world proportions, although with no sign of corresponding sales. These high-price sales are the tip of a very large iceberg.
Most transactions take place somewhere in the depths of the 'berg, well below the water line.
You may make some money if you pick a good domain name, but you are not going to get rich by selling domain names. Difficult to tell. On the one hand, there have been a number of high-profile sales recently. Ah, you're not going to draw me on that one. Their services are broadly similar, although it is clear that some brokers are larger than others, BestDomains for instance.