I am a complete novice at all of this but I think it is very hard to judge people sometimes and you do just have to use gut instinct. If I was ever unsure, I would just say no - there are plenty more potential cat slaves out there who will give them great homes!
I know first hand how hard it is to start breeding and getting your first lot of breeding cats in but this is why I have been as open and honest about my intentions as I can at the start and built up good relationships with (most of!!) the breeders I have managed to get coonies from. I remember making countless calls and emails to one breeder before she would even give me a definate yes but it was so worth it and I am now getting my second coonie from her next weekend
FCL