Some major retailers raise the online prices of certain goods days or weeks before marking them down in seasonal sales events, the NBC News Price Tracker shows.

In one corner is Amazon Prime Day. Amazon will run four days of sales, starting on July 8 and running through July 11. In the other corner is Walmart Deals. This event also starts on July 8 but, unlike Amazon, it will go through July 13, giving shoppers two extra days of deals.

Walmart is holding a "Walmart Deals" sales event to compete with Amazon's Prime Day. The Walmart Deals event offers discounts up to 50% on various products, including tech, outdoor gear, and fashion.

One more thing I found while ping-ponging around Walmart’s sale pages this week: This OB2 scanner from Nexpow. It’s going for $28.79, a great deal off its list price of $79.99, and has far more functionality than any of the $30 bottom-shelf units you’re going to find on the rack at an auto parts store. Could be worth a look!

Amazon Prime Day, the two-day mega shopping event happens Tuesday, October 8 and Wednesday, October 9. Not to be outdone, competitor Walmart runs its Holiday Deals event October 8 through October ...