Like most retailers, NewEgg has to resell the unit. Just because you think there's something wrong with it, doesn't mean there is something wrong with it. I ran my own consumer electronics retail business for 5 years and about 70% of returns have absolutely nothing wrong with them. NewEgg can't just throw the stuff away, they'd go out of business.
They also can't just send the stuff to the manufacturer. The manufacturer doesn't care about your issues and if you return stock of which 70% is functional for warranty service, they will kick your ass.
So you hire guys to test the equipment and return it to sell-able condition and sell it as an open-box return.
Back to our little problem. You bought a laptop. Great! You install Linux on it. Fine! Is it really that much trouble to return it to the same condition when you send it back?
NewEgg has to hire guys who sit there for hours installing Windows from the non-existent install disks (they don't include those anymore ... you gotta download them) so that they can recoup their losses? It would cost them more than the laptop is worth.
If the laptop is truly defective, and you can't install the original operating system as a consequence, NewEgg has no quick means of determining what you did with the system ... and the manufacturer won't care either.
So if you buy a laptop and decide to return it, return it to factory condition. It's the least you can do. Yes, tinkering with it probably violated some terms or some warranty. Do everybody a favor and keep it to yourself.