There are some amazing spokespeople, who happen to own or be the founder of their business. Colonel Sanders for KFC was so good they are currently attempting to resurrect him through imitators.
So far they have used Norm McDonald, Jim Gaffigan, and Darrell Hammond.David Alan Grier tweeted he was next.
The vast majority of people who attempt to become their own spokesperson end up as failures. The reason is they are simply not memorable. In Columbia JT is famous as his own spokesperson for his car dealerships. He worked very hard with professionals to cultivate that persona. Those of you who have met him know the real JT is rather reserved. Dave Thomas started Wendy's in 1969 because he didn't like any of the fast food hamburgers. 20 years later he decided to become their spokesperson because he didn't like the actors they were showing him as potential spokespeople. He talked about how he had to be pushed outside of his comfort level to get the spots right. It also took up most of his time. "Wendy's never would have made it, if I had to run it, and be the spokesperson".
There are some people who are really great at multiple things. But that's not most of us. Most of us have to work our tail off to be great at one thing. If you're running your own business, that's probably your thing. If you're going to invest all the money to buy air time for commercials, spend a little more to get someone who doing commercials is their one thing.