Can we talk about why everyone checks the PSU last when a PC won't boot

Had a customer bring in a tower last Tuesday that three other places passed on, and the whole thing was a dead 5V rail on a cheap 500W unit. I mean, I get it, pulling a power supply is a pain and nobody wants to do it first, but I've seen this pattern probably 15 times this year alone. The board lights up, fans spin, so everyone assumes it's RAM or the GPU and starts swapping parts for an hour. Ten minutes with a $30 tester would have saved all that guessing and the customer another $90 in labor. Maybe it's just me, but I always throw a known good unit on the bench before I touch anything else on a no-post box. What's your go to first step on a machine that powers on but won't show a picture?