Go buy a Certified Doubled Die penny. then you'll have something to compare and not be enthusiastic that everything you see is a DD. https://www.errorvariety.com/OFD/DDD.html https://www.errorvariety.com/Doubled-dies/index.html
Or buy a copy of the Red Book, which has photos of the most famous and well know DD. Or just look up photos of known ones online whenever you think you have one.