Why Use a Licensed Contractor?

At first glance, this looks like a perfectly normal gate attached to a block wall.

But look closer... the block wall on the right is tilted to the left at the top, by about an inch. That would not be unusual if perhaps if this block wall was 30 to 40 years old perhaps.  However.....

This block wall was built less than a week ago. (I built the gate) While I do not do block walls, the customer had asked me what something like this would cost.  I gave him my best guess, and he got some bids.  He went with the lowest bidder, a non licensed worker(s) and a friend of a friend.  So I guess he got a great deal.... or did he?

So... either the wall was built out of level to begin with, or, whatever foundation used was not strong enough such that it shifted already.... wow!