I don't understand the payment formula based on what you have written here. Of course that doesn't matter -- no one needs for me to understand it. But if I can't understand it from what you have written, I have to question whether you are sure that you understand it. And are you sure that you and the professional making this offer both have the same understanding in mind?
No legal advice here. READ THIS BEFORE you contact me! My responses to questions on Avvo are never intended as legal advice and must not be relied upon as if they were legal advice. I give legal advice ONLY in the course of a formal attorney-client relationship. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. That relationship is established only by joint execution of a written agreement for legal services. My law firm does not provide free consultations. Please do not call or write to me with a “few questions” that require me to analyze the specific facts of your history and your license application and prescribe for you how to get a State license. Send me an email to schedule a paid Consultation for that kind of information, direction, and assistance. My law firm presently accepts cases involving State and federal licenses and permits; discipline against State and federal licenses; and disciplinary and academic challenges to universities, colleges, boarding schools, and private schools. We take cases of wrongful termination or employment discrimination only if the claims involve peace officers, universities or colleges.
From your question and from your comment to another posting, it sounds like some form of hybrid contingency fee arrangement. This kind of thing can get quite complicated and your description is not sufficiently detailed for me (at least) to make any definitive suggestions. The terms and conditions of the deal should all be spelled out in the Retainer Agreement you signed (or have been presented for signing) with your lawyer or law firm. I suggest you sit down with somebody at the firm (ideally but not necessarily an attorney) and make sure that you 100% understand the terms and conditions of the Agreement. Ideally this would happen before you sign the Agreement, but if not, you really need to make sure that you understand the terms and conditions of what you will be bound to honor.
Echoing the comment of another poster, if you think that it is a good deal then you should take it.