Identifying a crate motor

Hi all new to this anyway trying to identify what makes a crate motor identifiable what they use serial numbers on the block or vin numbers. Looking to purchase a motor and the gentleman says that it's a crate motor no paperwork no crate so I'm just trying to figure out how this becomes a crate motor as opposed to a truck motor or car motor it is new.
All crate motors come with build specs, and paper work including a cam spec sheet and usually a dyno report. I don't see why anybody who buys a crate motor would get rid of that documentation. So, might be a red flag.
Ask him which company he bought it from. Try to get a serial number from the block and call that company. They probably have a privacy policy, but just explain you are only trying to confirm whether or not it came from them. It's worth your time to do your due diligence, could save you from a disaster. Heck, if it's a recent motor, it may still be under warranty!