Personally I do not have any problem accepting a 'gift'. I undersatnd that to accept a gift graciously is the best way to thank the 'giver'.
I also understand that in my own business (in the crafts) I am not expected to give my 'time' for free, and so I, in the case I mentioned cannot expect my reiki giver to 'give' of her time for free.
What I would be uncomfortable with if I had not paid in £ is to then return, maybe several times, and await my 'giver' to have to ask me for payment, as any working person eventually must.
But I agree that an exchange is not actually necessary. Though I do as someone mentioned, think back to my first readings of Dr. Usui's experience in 'giving' unconditonally and how his attitudes changed thereafter.
Hugs,
Stylus