Not as bad as seeing Sinding alive and well across the bridge from Riverwood, in full daylight, after you have killed him and are wearing his skin. Gosh, a veritably singular innings of happenstance.
Maybe he tried talking to you when you were fast-traveling. NPCs do follow you into buildings when they're not done talking with you and you enter a building.
I like to believe that Belethor is a dangerous and a very shady character. He has a secret room in his store with a stock of dead bodies and if you are a necromancer he will sell the bodies to you, for a price. He wasn't kidding about, "If I had a sister, I'd sell her to you in a second."