Clients that don't understand what "at discretion" means.
I offer anal at discretion, and the amount of guys that text me and ask ahead of time can they definitely have anal in the booking is unbelievable.
I politely reply no, as this service is at discretion, so even though I may sometimes offer it cannot be guaranteed. My offering anal depends on how I feel, if I'm in the right mood, if I'm turned on enough, if I feel the client can be gentle enough. I tell them clearly when making the initial enquiry that this is a decision I make during the booking and not before. My profile also very clearly states that anal sex is at discretion.
Despite this I get endless "but will you"? and "I have 7 inches, quite thick so will you do it"? type calls. I really think that guys expect me to have one of those post office plastic things with the letterbox shaped hole in it - you know the ones they use to ascertain whether your letter will be charged in the cheaper or more expensive bracket, depending on whether or not you can squish your parcel through the gap.
They want me to say yes - if you can stick your throbbing purple member through this bit of plastic with a hole in it, this will qualify you to fuck me in the arse.
Anyway, if I was (for example) happy to bum-fuck anyone under 6 inches I would simply say so on my profile. That's not what at discretion means. At discretion means you have the right to choose, at any time, and for any reason!!
Rant over 
H xx
The guys who say they're 7 inches or whatever are timewasters. I have never had a guy show up after giving me the measurement. Doesn't matter if they say it's 3 inches or 10. He's not showing up.
However, I did once have a guy inquire about my "anal at discretion." I told him that it came down to his size, circumference, and how gentle he seemed. He just said, "Oh, there won't be a problem."
Sure enough, guy had a tiny dick. But he didn't press the issue or give me a size one way or the other.