Cold calling. And other proactive forms of sales when they seek you out and actively keep trying to convince you that you need their product.
Bonus points if the sales person is unable to actually explain the product and keeps talking about “we don’t sell products we sell solutions”
Just reminded me of an argument trying to explain that arithmetic with floating point numbers is not always correct to a coworker who was a mathematician just starting in software dev.
In a mathematicians mind the fact that an arithmetic operation can produce inaccurate result is just incomprehensible