Get a contract written up for graphic design work, this is essential to protect you and your client.

Things to include in a graphic design contract are:

1. Number of sample designs. I normally limit this to 2-3, as too much choice leads to clients not being able to decide. Once the client has seen samples they have 2-3 chances to request very minor modifications or a blending of ideas in the samples.
2. Payment schedule (even if it's for a mere $25, have a payment schedule), I base mine on 1/2 on signing the contract (non-refundable), 1/2 on completion of job. This way you are covered if your client goes sour on the project.
3. The clients design brief, this needs to be in detail so you and the client know exactly what the client asked for.
4. Client requested major modifications. This is additional to any of the above and would obviously be outside of the clients design brief. This is charged at an hourly rate.
5. Cancellation, the client loses the 50% deposit and may be charged for any additional work exceeding the 50% deposit at the hourly rate.