I always get people who contact me after they have gone out to buy a puppy,only to have the landlord find out. I will never understand why someone would try to get away with getting any animal when they know that pets aren't allowed in the first place.
This really confuses me too. I get how difficult it is to want a pet and not be able to have one, but bringing in a pet that isn't allowed can get you evicted, and that puts both the owner and the pet in such jeopardy.
When Zephyr had been with me for a few weeks, I had a dinner party that included some friends and some acquaintances. One of the acquaintances offered to buy Zephyr from me. (What? Who goes into someone's house and tries to buy their pet?) I said he wasn't for sale, but that if she wanted a kitten there were a lot of cute ones at the SPCA. She said okay, and I thought she would be adopting from the shelter.
Turns out she figured out the shelter wouldn't approve her because she wasn't allowed to have pets in her apartment (which I didn't realize when I recommended the SPCA) so she bought a kitten from a shady backyard breeder instead.
I felt really guilty, like I'd accidentally pushed her in that direction.
Her landlord never did find out, but a couple of years later she and her boyfriend bought a dog. It didn't get along with the cat, so they rehomed the cat because, and I quote, "The dog was expensive." At least they gave the cat to a friend rather than a shelter, but still...
I didn't really keep in touch with her after that. There were a lot of other things about her I really liked, but that really soured me on her company.