I'm torn about something and looking for some opioions...
To get it out of the way... TL:DR I adopted some ferrets through Craigslist and they had fleas, should I tell the previous owner?

And now for the further details (because there's more to the story)...
So I got these two ferrets from craigslist, the people didn't really want to part with them but they got them after they got their kittens and since the ferrets came around the one kitten had been tearing himself up so they for some reason assumed that meant that the kitten was allergic to the ferrets and to find them a new home. Good news for me as I was looking for some ferrets (which is a complicated story in itself). So I go to get them, and the one looks a bit older than they said it was because he's petite (which I know happens, this isn't my first circus with ferrets) but he also had very thin hair on his tail, you can see pink easily, which can happen with a couple of the diseases they get later in life. This was still fine with me and didn't make me not want them (obviously since I took them, derp) but when I saw the kitten I was like holy smokes he's really having a reaction! He had a bald patch maybe 3-4 inches long and an inch and a half wide on top of his neck and about half of it was an open sore! These people also had 3 dogs and another cat and all 7 of the furry creatures were running around the house when I got there. The lady got really choked up about seeing them go, and she called me like 10 mins after I left but I was busy getting lost (over the state line and out of my comfort zone) so I didn't answer. I got them home and noticed they were itching a lot, like A LOT. I picked each up and did the hair blow back to see the skin and checked out their bellies, but there wasn't any indication that anything was amiss except the bald tail on the one that was itching the most. Just for peace of mind I stuck him in the tub so I could get him wet down and see his skin better (they're both white, one albino, one d.e.w.) he had some red patches here and there so I got out the oatmeal bath and laterhed him up and promptly sudzed up a flea. So husband went an got the other one and they soaked and rinsed and soaked and rinsed and we'll be sevin dusting them and the house tomorrow (we have 2 cats also, who aren't treated because they're strictly indoor). The problem is, this lady obviously didn't really want to part with these ferrets, but she was blaming them for what was apparently flea allergy dermatitis, not ferret allergy. So do I tell her? Do I offer her the ferrets back in n even exchange and go on looking? Do I not say anything? Obviously her cat needs some treatment, but I really don't want to give the ferrets back :(
What do ya'll think I should do?