How to get original specifications of computer system

Hi everyone, I hope you all are well :)

I want to buy a new computer, and there are many cheaters
in market :/. I don,t know how to know original specifications of a computer system. I heard that shopkeepers change the computer specifications with software's and with any registry method :/ ... by this method, computer do not show the original hardware specifications, but shows that specifications that are set through software, but computer speed is of original hardware. :/

so is there is any method to know about original hardware specifications like processor, hard disk, ram, graphic card etc...

Is BIOS shows original specifications if a person changed the specifications with software??

There are many software that tells about system specification like cpu-z, WinAudit etc.. is that tells original specifications after chaining specifications with software or by editing registry???

Waiting for your response
Thanks.....