are you still in touch with the previous owner?? could be a good idea just to give them a bell and ask what he was fed and how he took it,just so you could try and mimic the way he was fed previously. also i know this sounds mad but what colour mice are you feeding?? i had a corn that would not even touch a black or grey mouse but would nail a white mouse lol.
1.1.0 Central American Boas het 66% kahl albino (Male is Pedro and Female Bo)