Hiya.
I’m playing on the latest experimental (I update every couple of days or so), and I’ve noticed that when you’re in the buy menu for defense mode, on the tab with the “lighter” item in it, as you scroll up and down in that tab, the price of the lighter changes.
Lighters spawn with a random amount of fuel, it’s probably randomizing the lighter when you scroll, and the price is changing based on the amount of fuel. It could just enforce max charges for items like that bought in defense mode.