To be fair, Ive heard of some reasons to bid with these 'User ID kept private' ebay types.
In the past, in some cases ,'sellers' are targeted by nosey,vindictive, and irritating 'experts' pretending, and acting like some kind of ebay 'police' in that particular field.
They take it on themselves to contact buyers and 'put them off', Unfortunately some even do this to put off prospective competition buyers so that they can buy at a cheaper price !!!!!!!!
But in general ................. AS SOON AS YOU SEE ..........'ID KEPT PRIVATE' AND 'FEEDBACK PRIVATE' .............. then avoid them like you would MvR with the sun behind you.!!!!!!!!!!!!!!!! My observations over the years are that you are likely to be buying rubbish from a seller whose only interest is hiding from any sort of scrutiny........when ebay bans 'id privates' and 'private feedback' the better overall.
Ehrenpries