First off, the lens. Cheap cameras (the ones you see on Amazon for $20) use plain plastic lenses with zero anti-fog or water-repellent coating. When it rains, water sticks to the lens like glue – no beading, just a slimy mess that scatters light. You know that weird "hazy" look you get? That’s condensation seeping into the lens housing because they skip the rubber gaskets to save 2 cents per unit. I once took apart a $15 camera and smelled the cheap plastic – it was like burning plastic right out of the box. Disgusting.
Second, the head unit. Those (crappy Android head units) you see at auto parts stores? They skimp on image processing chips. Even if you have a decent camera, the cheap unit can’t adjust brightness/contrast fast enough to cut through fog. I had a guy last month who dropped $400 on a "premium" universal unit – it froze up every time it rained. Swapped it for (WITSON’s units) and boom – crystal clear. The difference? Real weatherproofing, not just a sticker that says "waterproof."
Oh right, one more thing – don’t get me started on the liars who P their product photos! I’ve seen sellers take pics of a camera in a dry studio, then claim it works in monsoons. Total garbage.