In such cases one can use front-loaded invoicing, meaning that the invoice can be sent before the commission has even been started. In these cases, it is essential to agree upon the due date by which the source text must be delivered to the translator and the deadline of the translation. It is also important to agree on how to proceed if there are budget overruns or deficits – who will pay for the difference in price and whether the possible deficit is paid back to the client or accepted as a loss (and kept by the translator).
Keep in mind that when the prepaid commission arrives for translation, you probably – and hopefully – have other ongoing commissions, even if you received the payment a while ago. It is a good idea to keep reminding the client about the agreed delivery date in due time, and to make sure that the source material will arrive on said date.
Invoicing upfront is easiest with regular clients that you know well since you both know the routines. An inquiry from a completely new client should be met with professional courtesy, and healthy caution – is the commission a sincere offer or is it too good to be true?
It is a good idea to use advance payment with very large projects and with new clients who you do not know yet, and checking the client’s credit score is always recommended. In these cases, you may also choose to use deferred payment, which means the client pays an installment after each part of the project is delivered.