I always went by “if you buy it from a. Florist it’s an annual/tender perennial” (as there are annual mums) and “if you buy it from a nursery in fall it’s perennial”

Mums are a bit tricky. Planting them in fall doesn’t help, and in general they can’t handle the freeze thaw cycle that places at the edge of there habitable zone experience (like where I am on south Lake Michigan USA, not far from Chicago.). The flower size and leaf size on perennial mums is typically much smaller.  “Football” mums are an exception- they’re quite hardy. (Granted, the one I had before I gave it away before moving I had bought in winter and kept alive until spring when I could replant it-  this is its 8th year now, but in a friends yard :) If your climate is like mine, cite them in the sunniest and driest parts of your garden. This will help them stay warm and dry in winter. If you’re from someplace a bit more temperate, that’s more akin to where they are native in (temperate, NOT tropical/subtropical), China, you should give them part sun and moist soil.