QA: feature not working
Me: Clear the browser cache
QA: it's working now
Me: 😎

So he *did* find a problem

No, qa should test each and every bug in clean browser to isolate problems. How do you know it's no a problems created by some other obscure piece of code that only happens if you do certain things before the actual bug. Then you have a problem to recreate the steps consistently. QA should always test in clean browser.

Engineer trick.

But the actual users of the page have cache too, you cant tell them to clear it.

My life in a nutshell...

@AlexDeLarge @Kekica for PROD we'll be having CDN and version upgrade of that will clear cache

I think Cache is a really annoying thing for programming. There are still too many web apps or platforms that handle cache badly or just have some error.
If it wouldn't be for session and form data I would disable cache everywhere. Our Internet speeds are good enough without cache.