why are there some whose identities are hidden--are they the stores themselves bidding against us?

[conkira]

why are some bidders identities hidden?

[dmil8030]

What you are seeing is a private listing, set up that way by the seller.  Yes, one of those 'private' bidders you see could be one of the seller's other IDs used to shill up her own items.  That is why a lot of people won't bid on those types of listings.  Ebay does not encourage them unless there is a good reason, see the following link:

http://pages.ebay.ca/help/sell/private.html

In those, you see your own ID but everyone else appears as 'private'.  That is how your ID will look to others, as well.

The other kind is when you see a user ID where the feedback is seen as (private) beside the person's ID.  That means the person has chosen to make his feedback comments private.  Only buyers can do this, - sellers have to have viewable feedback, understandably.  This link will tell you more about that:

http://pages.ebay.ca/help/feedback/profile-public-private.html

[scifan57]

Everybody but the seller of an item will see the identities of all bidders but themselves hidden. Only the seller of an item can see the user IDs of all bidders on his listings.

[secular-humanist]

this is a fraud loophole sellers still use.

certain sellers have a few "other" accounts that they use to inflate bids. eBay is very poor at catching them as of 2012 Sept, despite eBay claims, sellers are inflating bids.

If you notice the bid from a buyer with over 60% bids with one seller, you smell a rat. I've reported several 100% bidders that only bump bids on one seller, eBay has yet to get rid of these shell bidding abuses / fraud. Press hard to get eBay to honour NO SHILL BIDDING