Iphone 7 GSM /CDMA Limitations

I lost my US Iphone 6 in UK was told to purchase a replacement SIM Free, Unlocked phone so I could use both US and UK sim cards, the only unlocked version available at the time was an Iphone 7plus. The retailer agent did not inform me of any network limitations and it has taken repeated visits to Verizon store in US for them to work out that Iphone 7 models are programmed and installed with different network modems depending on where you purchase. Should this not be made clear on the packaging and marketing? AppleCare told me it was a store issue and the store say as it is not a warranty issue and more than 30 days so I cannot exchange, now I am left with phone that will not work on USA's biggest network . What is really frustrating is I would never had purchased this phone if either the retailer or the packaging had made it clear .

Why is this issue not made clear when selling /marketing this model?