How to tell what mods I've got

My new 06 Sti seems to have quite a few mods done to it, dealer I bought it from we're not that clued up on it either, have got receipts with paperwork for a few bits but car has more mods than that, how do I tell what mods it has as not sure what is standard bits and what is modded, salesman reckons it was 370bhp but nothing in paperwork to prove, it has got a receipt for a dyno run but no graph, it seems to have been remapped but don't know who by.

What will be the best way to find out what mods are on the car and not just engine mods.

Thanks

Try and track down the previous owner and have a chat.
I did this years back when I went to look at a Williams Clio (thought it was anyway). Was badged up and coloured as one but when I tracked the previous owner down it was a std 16v Clio...............

Bring it to the RR day and we will have a look over it