Within the Steem economy things are the other way around: you don't agree on a price per hour of writing, but you simply put in the work. Then, according to however the community values it, you might get rewarded.
I'd answer to my friends: here are the photo edits, here's the thing you wanted me to do and this is my account/wallet, if you feel like this should be rewarded somehow, feel free to do so, but OK if not.
On Steem, I think the culture is made for financial reciprocity so it is more accepted. In the case of the Steem friend, it was for a write that I would be get voted upon anyway by the community. In such a case, I can't justify taking payment on top with regards to my personal integrity.