I generally try to avoid Latin phrases, but when I encounter “quid pro quo”“quid pro quo” in English, I generally interpret it, perhaps wrongly, as capturing the notion of “the reciprocation/return of favors/actions” and my two preferred informal/familiar phrases for expressing this notion are:
“scratch my back, I’ll scratch yours” (always for favors) and
“tit for tat” (more neutral, sometimes for favors, but sometimes for vengeful actions).
“scratch my back, I’ll scratch yours” (always for favors) and
“tit for tat” (more neutral, sometimes for favors, but sometimes for vengeful actions).
These two English phrases lead me to the respective notions of “renvoyer l’ascenseur” (always positive, as far as I know) and “rendre la pareille” (neutral) in French.
Therefore, perhaps a French HannibalHannibal could have said:
“[Principe de] renvoyer l’ascenseur”;
“[Principe de] la pareille rendue/rendre la pareille”;
“[Principe de] renvoyer l’ascenseur”;
“[Principe de] la pareille rendue/rendre la pareille”;
or even, going back to the notion of “reciprocation” for a more formal option,:
“[L'idée/principe de] réciprocité” instead of “quid pro quo.”
“[L'idée/principe de] réciprocité” (instead of “quid pro quo.”)
(but see the clip provided in Kareen’s good answer as well as these two translations where Hannibal, apparently in two other scenes, uses “quid pro quo” in French.)