How to tell if an engine has low mileage?

i was told by a friend that if you remove the oil cap and look inside the cylinder head, if you can shiny metal then it has low mileage because it would be a dark tarnished color... is this true? i purchased an 01 crown victoria p71 with 87k on the odometer but the tittle states 99999 *NOT ACTUAL MILEAGE* as if it was unknown...... there is some rust in the engine bay but then again theres tons of dirt and debris as if it was never cleaned/maintained.. car runs great... btw