Can you promise a client true photo realism?

[hkezer]

About the contract, I try to incluude every single detail about the process result and payment, but almost everytime I discover something else. How do you overcome this? And also some clients just wait like 3-4 monts to pay(if they are huge company they wait even more, and you cannot even talk about it) how do you overcome it?

It's a crap assignment because even if you would end up delivering something that could be 'objectively' (by majority of laymen or professionals) judged as pure capture of reality, your client could simply decide it is "not his" kind of reality. Anything creative, is heavily subjective, who here didn't have client who would proclaim upon perfectly correct, highly realistic floor something in lieu of "I think it looks strange/fake, can you remove all the reflections and make it look super flat and ugly ? I think that's what the floor should look like".
Or my personal favorite "I don't think the mirror is showing correct reflection, shouldn't it reflect the other side of room" (Well of course, I will tell my renderer software to go back to geometry class).

This is why you have in you contract a clause that prevents this kind of argument, establishing quality that follows the common industry standard and the acceptations of limitation of technology.
It's ok to promise the best based on your existing portfolio, but not be legally beholden to unrealistic objectives.

[Juraj]

Saires touched up on perfect point, and that is the moment one party is aware the rendering is in fact..rendering, they look at it through different eyes, just like we do. They expect it to be wrong sort of, it's lot different if they saw the same image in some publication unaware of its origins.

2hkezer: Not sure I understand the first question correctly, but no contract can be predict every situation and mine is rather bloated already :- ). Good communication can overcome most issues that happens through process, though I can assure you with my best intentions, things still rarely go exactly as I plan. Regarding payment, I don't and never had this issue, but I take tremendous effort to choose clients, but this is off-topic here.

I btw, also like taking up on challenge, but the way the request is already worded gives up suspicions.