We need to be aware that just because an ancestor bore arms, does not necessarily give us the right to bear those same arms. The traditions of heraldry must be upheld for it to continue to be meaningful.
The terms "family crest" and "lastname coat of arms" are often misused to describe an armorial design belonging to an individual with a similar surname. There are hundreds if not thousands of unscrupulous businesses (typically called "bucket shops" by the heraldic community) that sell "surname" or "family" arms.
Keep in mind that arms are typically granted to an individual, and unless one is in direct line of descent (depending on the heraldic traditions of the country of origin), the use of ancestral arms by any other than those who have been properly matriculated, is fraudulent at best.
The sale of "surname" or "family" arms is a dishonorable practice. Unscrupulous vendors count on the perspective customer's lack of knowledge of the traditions of heraldry. To use arms that are not properly owned, usurps someone else's heraldic identity. Using someone else's arms without proper matriculation is fundamentally a mix of identity theft and property theft.