What can influence an artwork to become valuable?

there’s multiple things that can impact a paintings value.
Anything by a famous painter will be valuable (if Picasso signed a napkin It’d be worth millions).
another big factor is fame, the Mona Lisa wasn’t price less until it was stolen and got a lot of publicity.
Popularity, if no one likes a painting then no one is going to pay for it.
Rarity, if there are millions of the same painting the value will decrease because the painting would be easy to get.
When it was painted, lots of paintings values increase as they gets older, styles change, they becomes rarer, they become a part of history.

Generally spontaneous human combustion is something that still bewilders some, human combustion happens very rarely and doesn't affect the surrounding areas, so unless you want to set your self on fire, human combustion will remain spontaneous and very rare.

Idon’t think it’s true but if it is then you should make up a case then prove it