Ah yes, sea trials - what fun. With the boats we built, the buyer (and his crew) operated the boat during sea trials and a series of pre-agreed tests were performed by the builder (buyer witness) to verify performance and calibrate various equipment (ie: knotmeter). The buyer didn't feel we were fully qualified to operate the nuclear power plant that the buyer provided for the submarines we built. The key is to get agreement between builder and buyer as to what is going to happen when. Certainly the boat doesn't leave the builder until the buyer is happy, and there must be some warranty period where latent defects will be corrected. In our case, there was a period about 6 months from delivery when the boat would be made available for warranty work at the builders facility - usually minor stuff but not always.