Bike shops are allowed to sell any Ebike of any power. I know this because here in PA., the police set up a checkpoint 1/2 block from the shops that sold Electric bicycles and handed out fines dailey to the new buyers.
August , 2014 the law was changed here . It's written in the new Public Highway Law book. I think it's 1000watts output to the motors measured by a watt meter. This is what's happening dailey here. New Jersey is the same. In 2015, I rode my Ebike 46 miles each way, powered by a MAC geared hub motor.
(( I'm from California and I was going to move back but I changed my mind when I found out that Ebikes are not " Law Friendly" .