How much responsibility do I have for a cat poisoned by it eating my “Hawaiian Ti” plant?

I adopted a cat named “Bill” from Craigslist with the understanding that if Bill didn’t get along with my cat I could return Bill.

We have a big house so the two cats had plenty of space to sort things out. But the cats would have nothing to do with each other.
The Bill growled, hissed, meow, howled a lot and hid a lot. Bill seemed very unhappy. My cat was unhappy too. I could see after 4 days that this was a bad match so I returned Bill to the Craigslist cat owner.

I even let the Craigslist cat owner keep the $120 rehoming fee.

3 days after I returned Bill to the Craigslist cat owner, she texted me saying that Bill was sick and the veterinarian bill was $350.

Bill had obviously ate an equivalent to ½ a toxic Hawaiian Ti plant leaf that was in the large sun room where Bill was staying. I’ve had Ti plants and cats for 30 years and none of my cats ate the Ti leaves before.

I didn’t know that Ti leaves were toxic to cats. After all Hawaiians rap food in Ti leaves. So I googled the following:

“Hawaiian ti poisoning in cats is caused by the ingestion of any portion of the Hawaiian ti plant. The Hawaiian ti produces naturally occurring toxins, known as saponins, which cause the feline to develop gastrointestinal upset. Vomiting and diarrhea are the main symptoms of a Hawaiian ti poisoning in cats, but additional signs of central nervous system disruption may be present.”

So far I have paid the Craigslist cat owner $120 rehoming fee plus I paid the $350 vet bill for Bill the cat. All of Bill’s test result were normal and he should recover completely soon.

I expect that I’m going to be asked to pay more for Bill’s health care.

What do you think. Have I paid enough?