Okay' so when you order a pizza and you ask if they can put on a bit more sauce..

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83. customers should not be expected to "offer" to pay. vendors are expected to reveal prices.

yes, in this case, the customer could have headed off a problem by inquiring if there would be a surcharge, and perhaps phrasing it as "i don't mind paying a bit extra" would have been a particularly courteous way of doing this. however, the goal of any such exchange would be to establish ahead of time the existence and amount of any extra charge.

but this is at best an *optional* action on the part of the customer.
it's a *required* action on the part of the vendor to let the customer know there would be a surcharge, especially if it's not inconsequential.

i've been in or ordered at many restaurants and asked for something special or extra or unusual and invariably, if i'm charged more, they say "i'm going to have to charge you a bit more for that". they don't often tell me the amount, but they always initiate that topic and open the door for me to ask how much.

on the odd occasion when there's an unexpected charge on the bill, i pretty much always can get it removed simply by asking about it.