I tested this out on this site
http://dragonsfarm.host56.com/
It is using the latest version of the Mysidia script
You can send someone a offer of a pet for -999999999 from the trades page. The person accepting loses the money.
I made 2 accounts 1 named tittlemouse the other named avfctom
I send a offer of -999999999 tittlemouse from avfctom and accepted it and I got this.
On tittlemouse
You have -999996999 Dragon Yen.
Your links:
ADOPT NEW PETS
ACQUIRE POUNDED PETS
MANAGE ADOPTABLES