Some installers will completely refuse to install cabling under a mono block surface, and some only seem to carry a spade.
Combine this with the fact that need to get the job done as fast as possible to get to the next job (as they say they are paid per job, not per hour), and you can understand why some jobs are rushed.
Anything you value I wouldn't let them near!
For example, when they installed wiring underneath my hedge I'm sure they didn't even use a spade and instead pushed it under, as you could clearly see a bulge, and once it rained you could see the bright green trunking... I disconnected it and moved it to the side of the hedge where I could bury it.