Some people write in when they want to adopt and basically just ask where and when they can pick up the cat without even having seen it. Some people write in and ask a lot of questions - what should they do if this scenario occurs, which is better for the cat, etc? I take the second group of people any day. If people have a lot of questions, and ask even about specific items, you know they've done their research. The first group of people often does not - and may find that they are not ready for a cat after all.
If you are a foster, do make sure you sit down and guide a potential adopter through what having a cat really entails - you can make the potential adopter realise a lot of the pitfalls before they actually come to it. Even if they do not take your cat, you're probably better off knowing they're fully informed about it, rather then if they come back a few weeks later and tell you they can't handle the cat and want to return it.
For this reason, it's a good idea to have a trial adoption - it lets you and the adopter see if it's a good idea for them to keep the cat.