What you describe in not UBI, it's discrimination. I think it's pretty clear that if you exclude certain group from preferable markets, and sideline them to be able to buy only second-rate and third-rate goods, then you'll find plenty of examples where they end up at a huge disadvantage. It's not a test of UBI, it's a test of whether restricting access to a market can hurt a group against which it is used. I think we can all agree that the answer to this question is a definite "yes" - but it has no connection with UBI.