What to ask the previous owners?

Tomorrow night we are picking up our first snake. A 13yr old BP. The BP was a family pet and their kids are getting older and don't have time to care for the snake. We asked some typical questions, how does it like to be held, if it's in good health, reasons for letting it go. They are giving us the terrarium as well, so I am hoping the move doesn't cause to much stress. They told us its only been fed frozen rats, nothing live. It enjoys being held and has never bitten.

What other questions should I ask?

I would ask if it ever goes off feed, either seasonally or during its shed cycle, and how they feed it - off tongs or left in the tank overnight. That's all I can think of off the top of my head, seems like you've pretty much got things covered!

Well first no it does not enjoy being held that's just what some pet owners think.

The questions to ask are

Feeding habits which includes prey type and size as well as frequency and also fasting.

Health history covering the last 13 years.

Husbandry which includes how the animal has been kept for the last 13 years (temps, humidity, substrate), this will let you know if the animal has been kept properly for 13 years but it will also allow you to mimic the same environment so the snake settles down a little faster (granted it was kept properly of course)

This all assumes people are telling the truth. I always want to believe what people say, but if it is a pickup from a random seller I would take what they say with a grain of salt. Since you don't have other snakes you wont need quarantine, but just keep an eye out for any health issues, coughing, mucous, mites, etc.