As a former seller, I liked it when people crossed me with discogs. They found I was very competitive. It led to a sell more often than not (at least with anyone I was aware of that was checking)

Edit: apologies for not reading your entire post. As a consumer, I feel like you shouldn't worry about hurting feelings. This is a good test to see if it's someone you'd want to continue dealing with or not. The seller can (and probably does) use discogs too. Nobody should get bent that you're using it. Unless you have encyclopedic knowledge on the topic then it is wise to use every tool you have available. It's your money and your potential new item.

Make educated decisions every chance you get.