But what is the ideal waiting time that I have to consider to re-pop the review message when the user choose 'remind later'?
I also think that after they make the next deal using the app makes the most sense, for two reasons:
If you choose an arbitraty waiting time (say a week), there's no guarantee that the user have used the application since and thus has a different opinion of your app. This holds true for any length of time you choose, it's possible that the user won't even open the app in months. If they didn't want to rate it back then, why would they want to do it now if they haven't used the app since?
I would argue that when they've just made a deal (successful or not) is when they really have something to say about your app. I know that as a user I would be more likely to positively rate an app after I've just used it to close a deal and make some money, than if I'm just being harassed by pop-up every few days
is it acceptable to send users who choose 'never remind me again' a new reminder message ?
No, as a user I want the option to not be reminded and if I select that option, the last thing I want is another reminder a few days later.
If you keep bugging me for my review and will keep showing pop-ups until I do, I'm much more likely to just leave a negative review to be left alone.
If you're worried that a user will click the "never remind me" initially just to get rid of the pop-up and that they might want to give you a favorable rating later on, a solution is to keep a "Rate this app" button somewhere accessible in the menu.