Welcome to Just Answer and thanks for your question. Despite what those sites online tell you, a crest belong only to direct descendants of the man who originally earned it. Just because someone's name is "Stratford" for instance, doesn't mean that they are entitled to use any heraldic devices issued to the original owner. All the "research" sold online entails is looking to see if someone of the same surname has ever been issued a crest, coat of arms, etc. It has no meaning.
To determine if you are entitled to use such a device, you should contact a certified genealogist who can trace your ancestors (hopefully) back far enough to determine if your direct ancestor actually had a crest.