That's great, unless the store you're in is a giant concrete bunker.
Mobile data barely works in my neighbourhood supermarket; even text-based communication is frequently dicey, but you want to send someone a photo of something as a "should I buy this"? Fuhgeddaboudit.
Why open yourself up to all the nasty of public WiFi for that?
Either you're buying something cheap, so just do it. Or it's something expensive, and in that case a simple quick message isn't really enough. Go out to the parking lot and talk about it, or come back later.