All kinds and all qualities of teapot are manufactured in Yixing, from the cheapest mass-produced molded vessels to the more expensive handmade artisans' wares to genuine art works (US$5,000 and up) that were thrown and hand-finished by lauded potters. Most commerical Yixing pots are machine-molded using a significantly lower grade of clay -- frequently not zisha (the famous "purple clay" of that area) -- and many are not fired at the proper temperature. In terms of design, these commercial teapots' flaws certainly do not render them unusable, but the defects can be annoying to someone who is accustomed to preparing gongfu cha with an adequately-made teapot.
In any case, the fact that a pot has originated in Yixing says virtually nothing about its quality or functionality or value. (Some excellent teapots are being made in Taiwan, too, by the way.) Only someone who is reasonably experienced in identifying pots and clay could tell you whether it's a decent vessel, and only an expert could declare any stamps or signature marks on the pot to be informative and genuine. The least expensive factory-produced pots often bear a "made in Yixing" ideogram stamp (even if they weren't), and artists' chop marks on higher quality pots, including antiques, can be forged or faked, so unless you know exactly what you're looking at/for, the presence or absence of identifying marks is literally meaningless. Hence the conventional and sensible advice: Select an appealing teapot that you like and can afford, and don't be influenced or impressed by claims of origin, quality, age, clay type, value, or authenticity.
:I appreciate your help. If it's a useable pot, I'm going to try :Cameron's baking method mentioned in another post. (I think.)
You'll only know if it's usable by trying to use it. Make sure to "cure" it first until the taste and aroma of clay dust are not present in your tea. And unless you're prepared to lose the pot, I wouldn't boil or bake it; even higher quality teapots that were imperfectly fired (or that contain a large, visually undectable air bubble/pocket in the clay itself) may crack or burst when subjected to that level of heat.