Still reading my last request, but I keep forgetting to jot down this one so I can read it next.
Kind of an older story about a brother and sister. She makes him give up his allowance for favors, but he ends up so good that she starts paying him, and he ends up with of his money back as well as hers. I thought it might be a Lubrican story but I went through his stories and didnt see it (though, given how many he has, it is possible I missed it)