Good insight into the buyer's perspective. It's fairly clear that you have a more intelligent strategy when it comes to selling on Ebay than the buyer I dealt with. It seems like RJ's perspective is probably his strategy for selling, which is probably a reason for his response to my offer--perhaps more out of frustration than anything. As I told the buyer, just a simple "decline" would have sufficed, but I just couldn't leave his accusations about me alone, especially since I thought (and now confirmed here) that my offer wasn't unreasonable and deserving of such vitriol.
I never message sellers asking for their lowest price. When I see a buy it now and make an offer options, I assume that the seller is willing to negotiate, so tend to offer a price about 10-15% less. Now if the buyer has a card that is well priced above others for the same card, I might offer about 25% less, or just even go to that seller depending on the card's condition, shipping, delivery time, etc.