Do you bargain when you can?

Of course. There's nothing like a good bartering session.

When I was 10 I haggled with some fella for Italy vs. Norway tickets at the World Cup (France '98).

If I'm ever in shops that are sketchy, like in markets or often in other countries, I'll always barter. The prices they say to you are often more than double the value of the product, bollocks am I paying that!
When I was in Mexico I haggled with a vendor who was trying to sell me a silver chain necklace for $120 talked him down to $25.
It depends on the original price of the thing

If its off a car boot and its a console and the bloke says fiver ill take it
You cant really beat a Dreamcast for a quid