Let us see it from a cost-efficiency point of view. We have that every unit of the first selles costs 40$. But the total cost might be higher, since there is a chance for defect. On average, on 3% of the cases the defect will happen and it will cost him 500$. Hence, on average, a fence unit from producer a costs 40$ and has a repair cost of 3%*500$=15$. The total thus is 55$. For the second provider of fences, the standard cost is 50$. Similarly, the average repair cost is 0,5%*500$=2,5$. Hence, the total cost per unit is 52,5$ (total cost=upfront payment+repair costs). We see thus that the lady should win the bid; even if you pay more upfront, the difference in durability makes up the cost difference.