Not sure if domains buyed for $300 are premium domains. And it is very tight line between $20 and $300 price. If nobody see the domain you will buy it for $20,or $60 if you are using dropcatch service. If you are biding with someone, the price go up, and in 90% in biding will be included hugh domains or other bidders which are "overpaying" domains. Premium domains are domains which you pay over $1k with properly knowledge.