I agree with those that view the plumbing as substandard work. It is hard to imagine how there will be enough depth for a proper paver base or adequate depth for the freeze protection you will occasionally need. This is the very reason why buyers should include details like minimum depth of pipes, electrical conduits, etc. in the contract.
PB's are always saying they have never had an issue with this or that.
If this were my pool, I would hire an independent in the industry, someone with IG gunite experience, to inspect at each stage. The idea is to keep an eye on the PB. In the total scope of things, it would not be that expensive. The quality of this PB's work is highly suspect and you need to be proactive.
Good luck.