If the data is so valuable that you are this worried about it, then forget about the manufacturer's credit. It is possible to retrieve data from "demagnetized" surfaces using advanced techniques. It's also possible to retrieve data from disks that have been overwritten once or even twice with zeros, and even in some cases when overwritten with random data.
When I was a "spy", we disassembled disk drives and sanded the oxide off the platters. That met government requirements for destruction of data. Then we'd play with the magnets for amusement. Too bad about the $3000 of technology that got wasted, but the data was far more valuable.