I think it depends on your ad. If you claim to be a GFE, I'm not sure I'd appreciate any upsell at all; certainly not $100. If your ad specifies a variable menu, then, MAYbe $100 upsell, especially if the normal meal is $500/hour or more. I will admit that I'm not familiar with your regular menu.
But in my admittedly limited experience I've never seen ANY up sell more than $50.

but I just have never felt right about an up charge for a particular activity in this hobby.

A)  GFE rarely includes Greek.  PSE is sometimes considered to include Greek.
B)  For non Porn Star and/or Major VIP escorts the up charge for Greek is normally $100
C)  For Greek with Major VIPs and/or Porn Stars the rate for Greek will range from $100-$500 depending on the lady, and is normally booked in advance.
D)  However, there are some Porn Stars that dig Greek so much and may dig you so much that they expect you to perform Greek on them.  My two all time favorites (A.D. and A.B. (you can check my reviews)) would expect me to please them in a Greek way or would be very disappointed with me

...be referred to as an "upcharge."  An upcharge is an unexpected fee that the provider tells you about after you booked a session and showed up, only to be surprised by an additional and unexpected fee for a service you thought was included.

And, while some gals don't have a dual rate structure, I'd say most in the northeast do if they offer Greek.  And most of the time it's $100.  I'm not saying it's universal, just that's what's norm near me.

As for your definition of "upcharge," I agree yours is correct but don't think the term must be used exclusively that way.

i hate when providers include a charge for a specific sexual act.  I understand the prep and effort and want to make sure that is properly compensated, but requiring a guy to pay money for a particular sexual act is a problem.  It is totally inconsistent with the idea of paying for time with a companion rather than paying for sex.  That is a critical distinction that, in my mind, crosses the line between legal, adult entertainment and illegal prostitution.  Especially if that rate is included on your website....

Re: I Think My 'Naughty Place' Is Worth 1k XXXtra (joking)

Your Welcome!

I am a VIP (I post in discussions under an alias), and I stand by my recommendation.

problem solved

women over 50 should just have a rate of $300.

I pay for a specified time of companionship...and if the lady likes anal, I'm happy to oblige.  Otherwise, I'll be happy with some "vanilla" companionship.

If they are charging more than 100 they probably do not like doing it and that will show, so why pay more unless you just want to feel you "owned" the girl.

While I see why an additional fee maybe disheartening to a hobbyist. I am going to play devil's advocate. What about those who don't care for greek? Should they have to pay a premium rate when they don't partake in that particular activity? Could the additional greek fee be in the event it happens rather than prepaid? What if it just happens to be an off day and not work out?  Should the lady return the additional fee in the event she didn't deliver as promised?  

No matter what a ladies site says or doesn't say. If she gets caught up in a sting, the minute she accepts money period, they are taking her to jail. Sometimes they will cuff a lady before that. So it's irrelevant.