I was in a game shop pretty much every afternoon five days a week for a large chunk of 1999-2000, and Dreamcast stuff was flying off the shelves-- until the boot disc appeared. After that, hardware continued to sell, but software dropped back slowly.
Sega's bad record had actually started to fade from peoples' minds, then the piracy wave spread. It wasn't more than a week before half the people I knew online or offline knew about the boot disc. (Recall that the early DC piracy required a special boot disc because they didn't know how to easily reproduce the boot session.)