we dont have that problem here, you buy it you have a warranty, done. its junk yard engine, why in the world would it have to be installed by a certified mechanic.
3 dead engines in a row, i for sure would want my money back, and then go shopping else where.
you dont know me, but i would be up the junk yard owners ass demanding satisfaction. threats of law suits work well too. make sure you have all your paper work form each engine.
in the long run, the guy at the yard dont want to go to court because that will cost him more than trying to make you whole.
if you have to call the cops and make a report at the very least, charge him with fraud. that will get his attention.