The biggest problem I've found with the various brands of non-pressurised paraffin wick lamps is operator error.... Or as I like to put it "other people messing with my lamps"
I used to take a few away to events to supply lighting in the 'In-Character' areas (rather then using electric lights that just look wrong and screw-up your night-vision), some people just didn't know how they work or basic troubleshooting.
The commonest errors were:
Putting it out by winding the wick all the way down, sometimes dropping it into the tank
Letting it smoke (wick too long) so the glass soots up
Turning the wick up too much
because its getting dim due to the sooting
Running them dry, then burning the wick trying to relight
Knocking them over/down and leaving them
And my personal favorate. Deciding that its too bright for the 'ambience' and draping a piece of gauzy fabric over the top
Bungee: PM incoming