My problem is: why do you think this is called "doing them a favor"?
Also... if a cop lets you off with a "parking ticket" instead of a $500 fine for speeding, do you deliberately pay the fine late so you'll owe more money as "hakaras hatov"?
as i understand it (maybe i am wrong) ELAL must pay something to AA in order for AA to credit a bunch of points to someone flying on ELAL, no? so i save the ELAL company a few bucks.
this is of course very different than getting a parking ticket, here ELAL provided me a huge discount with full and excellent service like a full pay person. While i'm sure many people give a cop a few bucks to try to lower their ticket, speeding tix are based only on if u get caught and the decision by the cop. acc to u i should just send in money to the city everytime i speed regardless if i get caught. again, the cop does not provide a service, and its not a special situation with appreciable benefit provided (could have also not pulled me over), for which one could easily tip the one providing the "service" (can't pay him, against the law).