How Much for Post Cards

I have an art store that wants to purchase a photo file one time so they can sell post cards. The credit will be on the back of the card of course but what is the pricing model for this?

I have no way of knowing whether they will sell 10 or 1000 or more of these post cards. Even if I develop a contract I have no way of policing it.

So some pricing scheme for the file would be appreciated...

No right or wrong answer just options.

Do a one time license fee and forget about it.
Do a one time license fee for a set period (2 years, 3, 5) Relicense again if they want when that expires.
Do a usage fee - offer a license for 500 , 1000, 3000, 5000.

The last option is more complex because you need to think about what you are charging for each card. It is perfectly OK to ask them how many they anticipate selling and do a license for that number - you just need to be charging an amount per card that is reasonable for both of you.

If this were a bigger deal I would suggest having an audit clause in your contract but I doubt the amount would warrant that.

thanks that has helped a lot!