Samuel Weller produced his popular American Arts and Crafts pottery in Ohio from 1872 until the company closed its doors in 1948. Today the Chinese are making reproductions that carry "Weller" marks, but Weller pottery is distinguished in more ways than just the stamp on the bottom. The color, glaze, size, style, weight and quality will tell you the truth about its history.
Purchase a variety of reference guides on Weller pottery. "Warman's Weller Pottery," "Weller Pottery" by Jeffrey Snyder and "The Collector's Encyclopedia of Weller Pottery" are just a few to start with. When you find a piece of pottery you wish to purchase, find the exact same piece in one of your guides or online and compare the features discussed in the following steps.
Compare the glazes. If the original is a matte glaze and the one you're looking at is glossy, you must ask yourself why. Typically the original pottery is only produced in one glaze. While the glaze may be a vivid green in the book, the piece you are looking at may look flat and faded, or the original may be soft and matted while the one you're looking at appears gaudy and bright. The accents and highlighted colors should be applied rather then slopped on, and the crazing should look natural, not even and uniform.
Measure your piece. Not everyone will measure things the exact same way, but if the original Weller pieces you have researched are 8 1/2 inches high and your piece is 8 inches high, that's a big difference. The one you are looking at is not original.
Weigh your Weller pieces. The original pottery was made from clay from Ohio. Today the reproductions are imported from China. The difference in materials and the process used to create the pottery creates a difference in the pottery's weight, with the copies being lighter than the originals. Also, remember that if a piece has been around for more than 60 years it will show some rubbing on its base where it has been sitting. But don't be fooled because someone can grind the base down in dirt and beat it up a little.
Look at the detail on your pottery. The detail of an original handcrafted object, though it was produced in quantity before 1948, does not compare to an object that is mass produced in modern times in an emerging market. The incising detail will be deeper and more defined on the original, while the fake may be smooth and filled with glaze. The original piece is a piece of art compared to one made quickly to fool the average eye.
Add up all the factors discussed here. If one factor doesn't fit but everything else does, the piece may be authentic. If all the attributes don't match up, you should be able to clearly see the difference between an original and a fake. If you find the piece at a yard sale for $1, don't stop and think about it, just buy it and have fun with it. If you're going to spend any amount of money on the piece, it doesn't hurt to ask the seller for a guarantee in writing. If someone doesn't want to guarantee a piece or they say they don't know whether it's an original, move on with your quest. There is plenty out there to find and collect.