Funn thing is - salesmanship is actually a very valuable skill, not many people can pull this off. Most people just think of it in a very negative way, and hire others with no skills or attitude. Then you get trolls like the guy in the store, and a sale is lost.
Yeah, my current job is based around sales, and making sure my staff push and get sales (and we've been very successful). However, my number one rule is this:
Tell the customer about the deal/product, ask them if they want it, confirm once more, then respect their choice. You're then giving the customer a good idea of the deal/product, but not going over the top and annoying them. You want them to return, not to never come back.
This guy in gamestation just wouldn't stop. Sure, try and get a sale - but don't piss off the customer, jesus.