Fair enough. I never said one Ebay coin dealer wanting to try to eliminate others made sense, (no barriers to entry, identical "location", endless supply, etc). So this example is not a great one. A better coin example I can make up would be one dealer with an exclusive supply of a certain series selling to other dealers, thereby losing his exclusivity and not driving traffic to his location. Not a huge deal, I just reacted that it "never" makes sense to not sell to competitors in business line.
I get it and agree with your point. A good example would be a show dealer with a lot of nice toned coins. He would prefer to sell to collectors and not spread his inventory out among competing dealers (and thus lose the status of having the best inventory).
I own a retail store. guess I can't buy coins from him/her, even though my stores aren't coin-related.
Yes costing himself three sales. Maybe more. I wouldn't care who bought it or why. Especially a proof set with one 40% likely non gradable coin
I wonder if he checks to see if buyers of his items are sellers and then what? Cancel the transaction? Lol