I went to Cape Verde on vacation a few years ago. It's an interesting place, where people from Europe, mostly tourists, meet Western African merchants, mostly from Mali, Senegal, or The Gambia, and native Cape Verdians. As a tourist, you can't walk 5 minutes on the island without being invited to visit a shop to buy stuff you probably won't need, but the experience is the opposite of what you describe. They'll invite you very politely, insist a tiny little bit, but then let you go with a "no stress" comment and a smile if you decline the offer. I think they understand the pointlessness and counterproductiveness of harassing tourists...

Most of my negotiations are with my 8yo, and usually are about bed time, when to leave the park or a play date to go home etc. We would agree on a time, then no one is allowed to change the terms without renegotiations. It usually goes like this

Him: "Can I have 30 minutes more?"

Me: "No, that's too much because so and so... I can give you 10 more minutes"

Him: "No, twenty"

Me: "I said 10"

Him: "20, that's the middle of 30 and 10"

Me: "I don't agree with that, 5 minutes then"

Him: "what, you said 10 before"

Me: "now, I say 4"

Him: "OK fine, then 10 minutes"

Me: "OK, 10"