Please Bear in mind that Family Crests belong to lineages, not to families.
Someone named Guerrero may have received a Family Crest authorized by the King for his use. His son may use it, but his brother's grandchildren cannot. So if you find a Crest in a kiosk at the mall or at the corner drug store you may be taken for a ride. Do not waste your money on dime-a-dozen fake diplomas giving you a description of some other lineage's coat of arms while yours may either be different or not exist at all. Not everyone has a Family Crest.
Yo have to find out if it was your direct ancestor who received the right to bear a particular Crest, and even then the purist will say, only the eldest child. (It used to be the eldest son).