It's a lot cheaper for a retail shop to buy shimano groupsets grey than off madison.
You can often sell them at less than the trade price of UK stock.
Id still expect some checks and balances, but as a rule as the price gets lower, the checks get fewer
If it is fake they’ve done a stunning job of making the Di2 all work flawlessly , and the overall finish of the groupset is still perfect after 4K miles so I still believe it to be real.
Never had a doubt as the place I dealt with wouldn’t be dealing in fakes with the stuff they sell.
Apart from the noisy chain it’s been perfect.