Question, do you charge them for the time you took to meet the pet & learn about the pet & where the supplies are located?
Nope. That's a freebie.

Les is right, you also need to get the feel for prices by other pet sitters in your area. I was low-balling it because I've only done it for friends a family. Strangers or clients are another story. I would also look into boarding costs and try to reach a reasonable price. This way if they say it's too much, you can argue that boarding their pet would cost them far more and they'd be taking the chance of stressing their pet out and contracting fleas, etc. Explain the benefits of a pet sitter vs. boarding.