The Roseville Pottery Company hasn't been in business since 1954. Collectors consider them crudely made - poor molds and extremely poor glazes. The glaze on most fakes is very dull and lacks depth. The glaze is flat and does not usually reveal the clay color underneath. Handles on the repros tend to be thicker and details are not as refined.
Most shapes vary significantly from the originals.
Leaves on real pieces are brighter and stand out from the background better. Most of the background colors vary significantly from the original colors and the color of the clay is usually whiter than the originals. The Huxfords' book lists the various trademarks that Roseville used. Remember almost every dealer in the country knows what Roseville is, if the price seems too good to be true then it probably is. Know your stuff, don't take anyone's word for it, if YOU are not certain.