Bowman wrong backs 1952 & 54
 

These appear to be authentic errors - what kind of premium should I put on them vs regular cards? The owner wants an offer
Thanks

I collect variations and most recurring print defects front or back, but normally not wrong backs. You can find a lot of them offered on ebay but in my experience they do not normally command a large if any premium unless a major star is involved. Still a collector of those sets or a player collector might be willing to pay a small premium. I could be all wrong on this. Often am. There are many other variant/error collectors here who will surely have views

Al's pretty much nailed it. Unless it is a big name it won't sell for much.

Thank you both