Tiger, totally agree! I found a hard (and expensive) way that I had to be present when the contractors worked in my garden. You cannot leave them alone, not even for a moment! Even if you hire a landscaping company, they often don't know the plants. Most of them don't even know how to walk in the garden
That is my lacmus test; one can see right away if contractors know what they are doing by looking at how they move through the garden. If they step outside of the pathway without a reason, or without asking your permission, don't give them your business.