Thanks for the explanation.

We draw the line at paying transaction fees out of our own pockets, that's all.

Oh, quite right. I wasn't expecting you to, that's why I wondered how these costs got covered. I like the idea of the tip recipients having the option to tip you in turn for collecting the tips; very neat. I may not be the only one to read the web site and wonder how transaction costs are covered though so perhaps a little more detail somewhere for us pedants would be good.