I've been offered one in trade, and I don't know anything about them. What questions do I need to ask, besides the obvious ones about condition and function? What is the typical value range?

Thanks in advance for any comments and suggestions.

They were just selling for $500 from classic so I'd say that is the starting point for value.  I owned one I bought in 2012  (I believe) that was great, put a few thousand rounds through it and sold it but ended up regretting that.  I bought two from Classic this time around and they look just as nice as the on I used to own.  The only thing I would check is the receiver and ensure the inside rails are straight.  Waffen Werks receivers were known to have issues.  If it is an earlier WW with a NDS receiver I have heard no issues.  I don't think you will be disappointed at all.

Are the receivers clearly marked as to who made them? I haven't asked for any detailed pictures of the markings yet.

If it's built with nodak spud receiver and greenhills barrel like mine it should be gtg.  Later models with their in house receivers had issues.

He says it's a Waffen receiver and barrel, and it runs 100%. Still on the fence about it.

Sound advice here.  

Stay away from later Waffen Werks ak-74s built on in-house, out-of-spec receivers!!!!!!

Agree, anything else is a risk.