In the 20 years or so we have been in business, we have been involved in some gorgeous installations; Everything from 25 story rooftops to flush in ground concrete.
Having said that, we also seen some disastrous installations too.
One of our most concerning issues is when a concrete installer slopes the pad. Under no circumstances should a pad be sloped. If you have to slope the concrete around the hot tub because it sits flush along the foundation, that is fine, but the pad itself must be level.