That seems overly adversarial. 10% per week is punitive; not representing any real cost.
What you should do is charge enough up-front (as a fraction of the invoice or a flat number) and bill frequently enough that a client stringing you along for a bill doesn't really hurt you.
You should also have a few clients going at once so that a few weeks late doesn't mean a few weeks of lost work, because at the first sign of a late payment you switch to other clients.
And for your regular clients, especially ones that have trouble paying quickly (perhaps due to corporate policies), ask for a retainer so you can keep their projects at a high priority without sticking your neck out.
Professionalism and respect go in both directions. Even large companies don't necessarily have a team of people dedicated to paying your bills instantaneously. If it's a good relationship and they value the project and you make it known that prompt payment is necessary to meet the schedule, they will pay promptly. If not, then no amount of punitive late fees will change that.
What you should do is charge enough up-front (as a fraction of the invoice or a flat number) and bill frequently enough that a client stringing you along for a bill doesn't really hurt you.
You should also have a few clients going at once so that a few weeks late doesn't mean a few weeks of lost work, because at the first sign of a late payment you switch to other clients.
And for your regular clients, especially ones that have trouble paying quickly (perhaps due to corporate policies), ask for a retainer so you can keep their projects at a high priority without sticking your neck out.
Professionalism and respect go in both directions. Even large companies don't necessarily have a team of people dedicated to paying your bills instantaneously. If it's a good relationship and they value the project and you make it known that prompt payment is necessary to meet the schedule, they will pay promptly. If not, then no amount of punitive late fees will change that.