Thanks for the ideas! In the end, it will be whoever Carl prefers (assuming they are both reliable and have good references, etc). One is a guy and one is a girl, so I guess it will be up to Carl whether he prefers girls or boys (I don't know). I like the girl better just as a first phone impression, but then again I assume that women are more nurturing to animals, which is not always the case.
So far I have these questions:
1. References list, can I contact them? Are these all cat owners or are some dog owners?
2. What time(s) of the day will you be coming over?
3. How long do you stay?
4. Will you also get our mail?
5. Are you trained in any vetrinary way (certified, vet tech, etc)?
6. How would you handle an emergency? Do you charge anything for emergency trips?
7. Do you keep a record of your time with Carl (like a daily diary for us to read when we get home)?
8. Do you have cats?
9. How long have you been pet sitting?