Thank Them, and Ask Them to Thank You _ must be sincere Money is often a touchy subject, so politeness about it is a good idea. Your clients are paying you money that they've earned with blood, sweat and tears, so let them know you appreciate it. You should also invite them to contact you if they have any questions and, more importantly, make it clear that you appreciate their present (and future) business. Some people also welcome testimonials; for example, by adding, "Let us know how we did. Write a testimonial and sent to... " If you're building your website's testimonials page or want to complete the feedback loop, this is a great way to get clients to give feedback on your work. If they have suggestions for making the process smoother, it's also a great opportunity for you to improve.
About proforma invoice _ A Proforma invoice is an invoice provided by a supplier in advance of providing the goods or service. A quotation in the form of an invoice prepared by the seller that details items which would appear on a commercial invoice if an order results. It is more of a customs declaration form used in international trade that describes the parties involved in the shipping transaction, the goods being transported, and the value of the goods. It is the primary document to declare value for customs. It is not a true invoice, because the seller does not record a pro forma invoice as an accounts receivable and the buyer does not record a pro forma invoice as an accounts payable.