I agree. I (usually) find it less than helpful if the review talks about shipping problems or other non-product stuff. (most products can be sold by multiple vendors)

That said, there was one review I found helpful because the review said it (something physically large) was damaged in shipment even though they returned it twice.

Maybe there should be a workflow for "You are purchasing from <company x> 81% positive - would you like to see their reviews as a seller?"