Usually you're not required to record this in general, but you'd have to convince the police or the judge that you don't have it. If you just sold €1,000,000 worth of goods yesterday, the police might not believe that you (now) know nothing about this person. However if the cops ask for exact details about a €10 sale 15 years ago, you should be able to easily convince them that you no longer store that information.

Lying to the police/courts and obstructing criminal investigation blatently is, obviously, a crime. You shouldn't do it. Also if they get a warrent you are breaking the law by hiding that information.