Frankly, I realize you want to keep up a good business relationship with this person, but I would never *pay* for a favor. Especially when the party acknowledges that it is a favor. Repayment for a favor can be something as small as a thank you note, or as much as a reciprocation of similar value (i.e. someone buys you dinner, you later buy them dinner).

However, I find it laughable when, as DC said, someone masks a service as a "favor" and then only later asks you to pay. Not only was this "favor" done without your prior knowledge or consent, but in that case it is undoubtedly upon the shoulders of the person doing the favor to undertake all costs involved, unless you had asked that person to do the favor in the first place, which you did not.

If I were you, I'd go speak to this person privately and just explain that you find that this is less of a favor and more like backdoor extortion - paying for services rendered which you never approved previously but acknowledged when they were received.

Kind of like getting free work done on your house by winning a contest, only to have the contractor send YOU the bill months down the line.