In my opinion, if the customer never asks, you don't have to volunteer that you're an ESL unless you actually realize that your English language skills aren't that great and could be an issue. In your disclosure, it's fine to make the argument to customers that you're such an expert in the academic area that they should overlook any ESL-related language issues as long as you leave the decision to them based on your honest disclosure. The only thing that's not OK is lying to them about it after being asked; they wouldn't ask in the first place if they didn't care about the answer.
I practice exactly what I preach anytime a UK client says he prefers a UK writer. I may indicate that I can do the topic well enough to overlook that I'm a US writer, but I never pretend I'm UK-educated, such as by typing my emails in UK spelling. It would be easy enough to just use UK spelling and say that I'm UK-educated, but I don't lie to get anybody's business. Obviously, that's another concept that's completely
foreign to some writers on this forum, like one quoted below.
In my opinion, there are 4 types of ESLs in this industry:
1. ESLs who are genuinely delusional and don't know or believe that practically anything they write sounds like ESL to us;
2. ESLs who genuinely believe that subject-matter competence trumps their lack of English language proficiency;
3. ESLs who are completely honest about it when asked; and
4. ESLs who are too stupid and/or too rationalizing to understand that customers have a right to an honest answer to the question about their location and primary language of origin and who are too stupid and/or too rationalizing to understand that just suggesting writers be honest with prospective customers isn't the same thing as racial or nationalistic prejudice or hatred. (See below.) Some of them lie because they believe it's their right (and not the customers') to decide that their subject-matter competence trumps their lack of English-language proficiency. The worst of the worst (again, see below) actually admit publicly (in other threads on this forum) that
they lie because they know most American customers do care and would probably choose not to hire them if they're honest when asked if they're ESL.
I have the feeling you'd be happy with them wearing arm-bands, you fascist.
Only you, and your armband should have the entire text of your forum post where you justify lying to customers because telling the the truth when asked about being ESL makes it "unrealistic" to expect them to use you for their projects.