Honestly, if I get the sense a candidate is chasing the perfect code base, he or she probably would not get an offer. People like that leave unexpectedly once

Honestly, if I get the sense a candidate is chasing the perfect code base, he or she probably would not get an offer. People like that leave unexpectedly once their itch is scratched (or not scratched). Assuming that the candidate was extended an offer and asked to look at the codebase, I would require an NDA. I work in a niche market so you can't get the secret sauce in a sit down, but there are methods that can give you an advantage. For example, I worked at a place that did something they weren't supposed to be doing to gain a competitive advantage. To this day, 8 years later, despite working at several of their competitors, I still haven't seen anyone else do this thing. I haven't revealed this to anyone and I won't. We aren't doing anything like that, but we do have methods that I haven't seen till now.