Well jc I am all for washing out Cartos and getting weeks of peak performance out of them. It's difficult at best to tell anything from just looking at a Carto outside of a hot-spot blister on the labeling.
YouTube - Vapor4life Tips, Tricks & Fixes for Cartomizers (2:33 mark..burnt Cartomizers)
Outside of being burnt into the polyfill (tastes nasty) there are some tell tale signs such as juice leaking into the wick/air tube after 10 drops or so. This indicates that the wick tube is compromised and has a hole in it. In this case it is possible to have a burnt Carto without the burnt taste. In both of these cases it is best to retire that Carto and dispose of it.
The other tell tale sign is that the Carto simply fails to produce the normal volume of vapor and the flavor has become diminished. Discoloration around the Atomizer wire is not indicative that the Cartomizer is burnt and may just be a result of what type of juice you are using. In any case if you avoid burning your Carto you should be able to get weeks of great performance from it as long as you put it through a cleaning cycle to remove any carmelized juice.
If you do end up filling a Carto only to find that it is dead or not performing well you can always spin the juice back out of it. I have a video to show how do that as well if you like me to post it. If you are unsure about a Carto, take an empty juice bottle and fill it with water. If the Carto has been cleaned and is dry add 25 drops to it either by dripping or syringe (1ml) if water floods the wick/air tube....the carto is no good.
Unfortunately the Atomizer (like a strand of Xmas lights where a portion does't work) can start to break down and the only way to tell is through vaping it.
Hope this helps...
So Macho, I'm just curious how your previous statement below supports your reply above?
Here we have a new member asking a very valid question and your response not only fails to address their concern whatsoever, but seems to discount the OP and all the family members that wash out and refill Cartomizers.

Just sharing your deep heartfelt concern for helping newer users and not appearing as snobs.