Years ago when Amazon was still pretty new they tried a business strategy. The idea was they would track the purchases you made and offer you discounts on products similar to what you were buying. After some research by some concerned customers it came to light that Amazon was offering discounts on products you might buy, but they were also raising the prices of popular things you would buy.
For instance, I enjoy fantasy novels. If some new author came out with a fantasy book then Amazon would offer me a discount. However if Robert Jordan came out with the next book in his series, Amazon would actually mark that book up for me specifically.
This business model would fall under the label "EVIL".
The Dark Lord of consumer electronics decided they might try a
similar tact. If you went to the Best Buy web site and saw some amazing deal, you might be inclined to run to the actual store to partake. Arriving to the store, crushing despair awaited as the amazing deal is not present. You quickly run to an in store computer and pull up the web site to prove that you deserve the amazing deal.
Betrayal...
The in store web site is cleverly designed to not show the online sales and deals. This is called, a bait and switch.
There are two things you can do to armor yourself against such a tragedy. First, ensure that the deal is not 'Online Only'. Secondly, print the page out with the quoted price and date. That way you have something to wave about like a battle
flag when you confront Customer Disservice.