The clean concept is internationally standardised throughout the industry now.
But the there are are still blockheads who disregard the rules because “..Hell yeah, it’ll fly; We took much worse back in the day when I flew in...”
As this crew are about to discover; passengers have these things called “mobile phones” with great cameras these days.
PS. Refuelling with warm fuel is only useful for melting frost that has formed above cold soaked fuel. It won’t clear frost or precipitate that has formed on the rest of the flying and control surfaces.