In Persian culture, there is a principle named taarof in which if something is being offered to you, you must decline it, even if you want it. The giver will ask again if you would like the object but even still you must decline it. This process repeats one more time. Then, if the giver was offering out of politeness but didn't actually want to give it to you, he would no longer ask if you would like it. However, if on the 4th round, the giver asks if you would like the object, only then can you accept this object. However, this principle may raise 2 halachic issues. Firstly, the taker lies when he says he does not want it. Second, it seems somewhat like gneivat da'at. One is lying and making a good impression on someone but he does not really deserve this good impression. Here is the wikipedia page on it: https://en.wikipedia.org/wiki/Taarof
Welcome to complex Middle Eastern cultures!
Shulchan Aruch says almost this verbatim if you're asked to be chazan -- you're supposed to decline the first two times, then only take them up on the third offer. It's a sign of showing you're not trying to be arrogant.
Of course, this works when the person offering it to you understands this is the way the game is played -- which is what avoids the genevat daat issue -- you're not defrauding him if everyone's performing the same script. (It's suggested that often today, if you said "no" the Gabbai will think it's literal, and move on to someone else.)
Mind you, there's a difference between a "no thank you" or "that's really not necessary" (probably leaves some room for negotiation) and an outright lie like "I'm allergic to chocolate!"
On a similar note, the Mishna says two people can be haggling over a price. The buyer says I swear I'll never eat bananas again if I pay one cent more than $800!. The seller says, oh yeah? I swear I'll never eat apples again if I accept any price less than $1000! Then a few minutes later, they conclude at $900 and both sides walk away relatively satisfied -- and allowed to eat fruit. Everyone understands this is how the game is played.