This neatly summarizes the dynamics of so many client-contractor relationships. Takes real professional integrity not to exploit the information asymmetry, which I regrettably found to be in short supply in the building trades, at least in the UK.
This is true, but it can be improved. For example, offer a bonus for excellent air tightness and insulation, which can be tested once the home shell is complete. Hire an inspector 1 or 2 times to critique construction along the way.
If the agent insures the quality and is contractually bound to pay all expenses for repair and maintenance, that could avoid a major chunk of the principal-agent problem.
Good luck with enforcing the contract. The cost to prove the agent made the error (and not you or the manufacturer or time) and then other legal costs would probably almost always outweigh the cost to just fix the problem.
It might be possible to materially minimize the probability of error to have 2 agents, one that checks the others’ work. But that also will get costly.
> Isn't this partially what you pay your architect for?
There simply isn't a way to eliminate the principal-agent problem.