Blackwell Research wheels (who was owned by John Cobb) went out of business in 2008. I seriously doubt that the wheels had only 300 miles on them. Maybe the guy you bought them from had put 300 miles on them after buying them used himself. That's the hassle of buying off eBay, where everything has only been ridden on Wednesdays to the store and back by a 130 pound guy who never crashed them. It's hard to say exactly how long those wheels will last. . .but they look like they have some pretty good mileage on them