A blessing in disguise then. At least it wasn't a cowboy job, the work had to be done, and any future work is an investment that will see a return. As long as your dad hasn't been talked into writing a Will instructing that all his assets will be going to a cat charity :)
It does sound complicated because by letting them carry out the work, technically it has been agreed to.
If there has been no talk about money until this point, if your dad really does come across vulnerable, you could say he told you he thought that it was a free service for the elderly, and...