Koss installed: two furnaces and two hot-water tanks. The first hot-water tank failed just over a year. This he blamed on manufacturing defects and convinced us to get another tank for him. The first furnace he installed never worked correctly (ie. the house is cold). After months of complaining, he finally admitted that the furnace he installed was the wrong size for the house and it would never heat the home properly.
About 1.5 years after he installed another furnace, we noticed issues with it. Again, he blamed it on manufacturing defects. When it was explained to him that he installed the furnace wrong and there was no defect, he said he would come out to fix his mistake but we would be charged his travel time, and for his labour. (We did confirm that it was a installer mistake with the furnace manufacturer and another qualified installer. )
I can go on and on with this...we will not use him again nor will our friends and family who previously used him.