I wonder if it so problematic, to sell a faulty computer, 2nd hand, and really worry about data being retrieved, that is so sensitive?
Who is the buyer? Someone that can't afford to buy new, or for spares? They are buying for spares, as they don't work, what data can they get that can't be had by hacking a working computer, by an expert, with top end equipment?
I was given a broken computer recently, and I managed to revive the hdisk, It's got data on Win7 to boot, and lots of boring text regarding his B.sc. No passwords, no private data.
I think an attacker would prefer a server or such type from a business, rather than an individual.