Just so you are aware: you are still running, from Microsoft's point of view, an illegal copy of Windows 7
> whatever he thought would change it so it would say that it was not genuine
It isn't just that it is saying that it is not genuine, it is the fact that it is a completely incorrect version of Windows 7. Note that OEM SLP versions include additional code for checking the BIOS SLIC table. As a result non-SLP versions cannot be magically transformed into an SLP version by a few registry settings or other activity that a virus might carry out.
>He also told me that COA's only go on new machines
Oh dear. More uninformed rubbish.
>He didn't like that i was accusing him of selling me a fraudulent machine
He may not like it, but he
is. I'll repeat: no 3rd party system builder can legally install an OEM SLP version of Windows for resale. SLP can only be installed by the original manufacturer. A 3rd party system builder can, of course, install a legitmate non-SLP OEM version on an old or refurbished PC - but are then
required to provide the relevant COA (and yes, it should be stuck to the case). They should also provide you with all the relevant software to be able to reinstall the OS.
They have a number of other obligations. In case you want to take this further, and need some sort of backing beyond what people are telling you in this forum, here's the license that system builders have to agree to which outlines their obligations and deliverables: