Business minded sister

I'm Walter 27 and left university and got a great job, but my love life is non existence. So I masturbate to get off, I was caught by my sister Fiona 24 going to university and like me having to work to pay her way thru university. Fiona wasn't doing well job wise, she had a job. But it didn't pay enough to help her have spending money, rent wasn't required as we both live at home with our parents(I paid rent now I'm employed). I use to tutor to pay my way and as top of class I was in demand. Fiona is okay at her studies, but tutoring isn't an option for her. She doesn't have a boyfriend or even date preferring to put her career first. Our parents were out and I thought I was home alone and Fiona was at her job. But she wasn't as her workplace was being renovated and was closed for a couple of days. So I was laying on my bedding just starting to masturbate, when Fiona walked in catching me cock in hand as they say. She had a chuckle at catching me and asked for a book I had. I gave her the book and she left laughing a bit as she went. I was was just recovering from the shock of get caught, when Fiona came back in. I didn't have my cock in my hand this time, she asked me if I was interested in a business deal. What type of business deal I asked, she got straight to the point. I'm short of money and my workplace closed for renovation doesn't help, so I started wondering if you would hire me to masturbate you for a fee. I said I can that myself, I know you can I've seen you she replied. Adding but I would do it topless and only for twenty dollars a time. I was interested real tits are better than pictures, but decided to asked how about you get totally naked and masturbate me and I'll give you thirty dollars I offered. She thought for a time and then smiled saying forty dollars and you can touch my tits. Sold, when would you like to start I asked, now is okay by me she said and I agreed. This is where I tell you we're greatest lookers there are, but I'm about average and Fiona is better than average (good looking). She undressed and she joined me on my bed and she masturbated me for the first. It was okay, but I was a little tense. But more followed and she got better and better, no fucking or oral. But on my last birthday she allowed me to fuck between her closed legs she had oiled nd she worn her panties so no accident could happen and let me suck her tits. No extra charge.