Lift and carry is a really popular fetish. I am also quite tall so get asked for it alot. Before I did it I thought it was going to be really weird but I must admit I am a convert, it really was fun and strangely quite horny (maybe that's just me )

I have been asked to do this and done it twice! best work out I have ever had. Usually the men asking are small themselves and wont expect to be on your back the whole time of the booking. With one guy I got tired so got on all four and he just sat there... yes just sat on my back.... odd.

iv had a request to kick someone in the balls, and knee him until hes crying. 

I've seen the follow-up, but this is 'ball-busting' on BDSM sites. It's not uncommon for pro-dom(me)s to offer it as a service.

Ive had similar request  to kick a client but declined as I am worried i might get arrested for ABH afterwards !

If you can aim accurately and either have smooth shoes or use bare feet, it won't leave any marks.