You’re at the local Best Buy checking out portable GPS navigation systems. You’ve narrowed it down to the latest Garmin nuvi versus a less-expensive competing model, but you’re not certain that Best Buy has the best prices. Also, you’d love to know how other consumers rate the two brands. No problem. Just pull out your smartphone and launch your Amazon Mobile app, which lets you browse the brands you’re considering, read customer reviews, and compare prices of portable GPS systems sold by Amazon.com and its retail partners. The application even lets you snap a photo or scan a barcode from an item; Amazon.com employees will then search for a similar item available from Amazon. If Amazon.com offers a better deal, you can make the purchase directly from the app.