You absolutely can auction off your character or art for CS Pets/items and/or currency!
You are allowed to set prices if you want, but you don't have to.
If you want to see what people will give, you can certainly set up an auction.
Just make sure you post your auction in the correct forum.
If it's an art auction, post here:
Forum/viewforum.php?f=21If it's a character auction, here would be best:
Forum/viewforum.php?f=69Or if it's on the Oekaki, try here, but make sure to state it's an auction!:
Forum/viewforum.php?f=52