I volunteer for a cat shelter and I do adoptions. For some reason people have a tendancy to tell the truth instead of lying. Just get them talking about old pets. Laugh with them. No matter what they say - do not get mad. Just play along. Never ask a direct question. And most of all, act friendly, wear a smile, and play it dumb. I've had people blabber out some stupid things by accident this way.
~ Oh, I've never had a cat live past 13. (Why?) They've all been indoor/outdoor cats. (You do know any cat from this shelter has to be an indoor cat?) Only one of my cats uses the pet door, I'm sure the new kitten won't touch it.
[They didn't get the kitten, and they never came back to inquire about a barn cat.]
~ You can't have an indoor cat without getting it declawed. [I was unbelievably close to getting them to accept the fact that a cat can have claws and not destroy the house when another volunteer came by and started yelling at them. That destroyed my credability and hers. They put in an application for a declawed cat and we approved it.]
~ We have six cats, five dogs, and 8 horses. [Your clothes aren't clean and have holes in them, your kids look like they haven't eaten in a month, and you want a 4 month old kitten, why? Didn't say that, but thankfully they never came back.]
So yeah, warning signs for me are:
~ Too many pets that have passed away without an explanation.
~ Too many pets at home currently.
~ The behaviour of the person around the cats.
~ The behaviour of any kids.
~ Unstable living conditions. [ie. We're in the process of a move; I'm a college student at home for the summer.]
I don't worry so much if they don't have a vet if they haven't had a pet for a while or if this is their first. I don't worry so much about college students who are living at home or with a significant other. (I'm the former, and my first adoption was the latter.) We've even adopted out kittens to families with young kids. (This one family had a 3 and 5 year old, and they came out for a few weeks in a row just to make sure they were picking the rght cat. The boys were so gentle with the cats, and just kept asking question about how to take care of it, and how to tell what the cat was saying. The 5 year old was even going up to other people at the shelter and telling them about the cats. I was sold on the kids alone!)
Now, because of the overpopulation, we do let somethings go that would have been a problem in the past.
~ Allergies. If they say they'll try medicine and they'll live with it, then it's okay. About half the cats get returned, but that's still a lot of cat that are placed in loving homes.
~ Unfixed dogs. It's one that the volunteers are torn over, but our cats are fixed before they leave, and they need homes. We try to talk them into getting the dog fixed, but it's not something we rule out from the start like we used to.
~ Declawing. If they say they want to declaw a cat, they have to take one that's less that six months old and have it done immediately. They aren't allowed to take any cat that's older than that unless we have one that was decalwed by previous owners. I don't like this. Almost all the volunteers are against it, but while we grumble, it really does come down to declawing vs. euthinization due to overpopulation. We'd rather see the cat declawed.
Twelve years ago, when my mother was looking for a kitten, they had much stricter adopting guidlines. Home inspection, credit check, five references, a vet reference, radomn home inspections.... My mother threw a fit, cussed them out, and slammed down the phone. A LOT of people had this reaction, and the shelter and people who worked there became known as Cat Nazis. Adoptions practically halted competely, and they had to alter their policies drastically. There are still people who refuse to adopt a cat from there because they think the people there are all crazy PETA people. (There are no members at the shelter. They are some fanatical people there who will corner prospective adoptees for twenty minutes and try to lecture and preach to them. It's a great way to get rid of bad prospective adoptees, but really bad for business when they chase away the good people.)
Edit: Forgot to say that two kittens to a first time owner will probably work out better. Kittens do the best with a companion, and they'll focus their energy on each other instead of on the house. (Hopefully!) We try and talk all adoptees who are interested in kittens into taking two, even if their first time pet owners. We even offer a "buy one get one half off" deal to entice people into doing so. It's good for two weeks if they decide they need a second kitten, and about half the single kitten owners come back for a second.