I have no problem with a seller barring certain bidders (prior to the auction).It is probably better for all involved that these people don't bid on the auctions that they have been barred from anyway, but I don't know why the seller doesn't just email them instead of posting the ID's in the auction. I think it makes him look spiteful. I wouldn't want to deal with a Seller like him.

In the online world these barrings are a lot less likely to be related to race, gender or religion and more likely to be about personal disputes just because a persons race gender and religion are not usually obvious online.