I know it sux, but an officer has no power in this situation. I'm sure you signed a documents saying "Used, As-Is." If the dealer was honest, they would take care of you, but since they seem crooked, the only way to resolve it is to take it to court as a misrepresentation. (assuming you have the original add saying 135 psi)
OK... It happened, so let's move forward. If I was in your situation, I would double check the compression, and if it is low... I would just do a quick top end. Heck... you may get away with just putting in new rings if the pistons are good. If the crank is still good, there is no reason to do an entire engine swap.
If you do just a top end... you will still be into it for less than the original asking price, and you can have a nice running ski.
The other GTi you posted looks nice. BUT... you need to take it on a test ride, and you need to check the compression before you buy, and don't take the word of the seller.