Any laptop less than, say 5 years old, has the type of anti-theft measures built into it.
Modern laptops have multiple passwords that can be set. If you were able to reset a password on a laptop it MAY have been a BIOS password.
Hard drive passwords are not affected by the BIOS or CMOS. Additionally, some brands also have an extra measure to not allow replacement of the hard drive to circumvent a hard drive password.
All this would be fine if buyers of used laptops knew about these measures. Unfortunately they don't. So even if they know of suspect a laptop is stolen they think they can still use it.
The regular posters on this forum all know about this and respond accordingly. If a legal owner of a laptop has locked themselves out the manufacture is the best resource. Others are not willing to contact the manufacturer for obvious reasons.
I am always skeptical when someone has a laptop they can't access.