Exactly. And why I always collect on labor after I've finished to satisfaction.I wish I had the balls to experiment with other peoples money. If I told someone I would fix the problem and told them I would only guarantee the fix if I could choose the products used, and the repair failed, I would feel obligated to continue repairs on my own dime until it was fixed.
Now, if I told them there “IS A CHANCE” using these specific toilets will fix the problem and I can install them as an attempt to fix this issue, and expressed there were no guarantees, I wouldn’t feel so bad at charging foe further repairs because I did not promise a fix, I explored a solution with the customers full understanding that it may not be the required repair.
So depending on what he sold you, and how he explained the problem to you, depends on how much responsibility he should be taking for this.
Why is it your responsibility to be out 1500 when he installed the wrong parts and failed to get you the results that he explained he would deliver? If he wants to gamble, shouldn’t he be gambling with his own money?
…. Again, unless he expressed beforehand that this was not a guaranteed repair but rather an expensive attempt at a solution. That would be a different story, but it doesn’t sound like that’s how it went down.
If there is still time to do so, You could call the bank and put a stop on the cheques you wrote to him. It’s really hard to get some people motivated to do anything after they have been paid. Refusing payment is in some cases the best motivator (unfortunately), but only do that if he guaranteed a repair for that trade. If you agreed to this attempted repair then I suggest you take his advice and call a real plumber.