New Hatchling Passed Away

[Bogertophis]

... and the breeder said he was on hopper mice, though said he didn't know when he ate last because his wife does that....

That's a really lame answer & I'd stay away from any "breeders" that give answers like that. IF that was true, a good breeder -one that cared & was professional- would have checked with his wife & given you an answer. My guess is that this snake wasn't eating much or at all, & he knew that but avoided admitting it so you'd take the snake off his hands. Just saying.

And your experience with the snake showing fear of a hopper supports my guess. Probably never saw one before. There's a small chance that the snake was just stressed from being in a new home, & that's why he wasn't eating, but I would bet otherwise.