Firstly, don't EVER listen to a word the salesman has to say. They generally don't know their balls from their moustache, and will say ANYTHING and EVERYTHING to try and get you to buy the car, truth or not.
If you have any questions, ask us here, we'll give you the right answer.
In simple terms, the BOV basically vents the air the turbo is pushing into the engine when you step off the gas. The throttle shuts, and the air usually has nowhere to go except back through the piping and hits the turbo, forcing the turbo to stop, and spin backwards. This is called reversion, and is detrimental to turbocharger's lifespan... The BOV is an outlet for the air to go, so it doesn't go back through the piping and hit the turbo. It's a good thing.
The Intercooler is basically like a radiator for your intake air. Cooler air means denser air, which means more power and less chance of detonation. Again, this is a good thing.