Was it a flight booking portal, that shows higher prices to iPhone users?

yes... it's already happening...

Closer to how lots markets work in many parts of the world.

The number of very wealthy people shopping at Walmart is probably so small that developing this feature wouldn't be worth the effort.

Possibly not - in a future release it could also scan for expensive watches and hand jewellery as the punter reaches over to pick the product.

Easy, hire a poor person to do your shopping. Already happens!

identifying customers based on gait analysis and bluetooth identification (already widely implemented) will certainly lead to individual pricing