Is it against the rules to market your own art at a high price, for example,
Selling a simple head texture (not very detailed) for 100k?

no, but it sets a bad precedent,
if someones dumb enough to pay that, then well done to you.

The important thing isn't about what you're selling, it's about how you're selling it.

I've sold head textures that were done in MSpaint for over 10k and i'm still confused how i did it.

It's worth however much someone will pay for it

Ive sold a few simple head textures for 75k it boils down to much the buyer wants the head

No, but how all the others said already if you find someone stupid enough to pay a shit amount of TC or money for a shitty art then gratz.

K cool(:
closing.