I am.
I'm the guy who wrote the story, maybe I did a bad job. It's not like they're getting violent or "trying to extract money from me" - jeez, when you do buy something you can just hold out a handful of money and they'll take the right amount - extremely, extremely honest.
In reality, they're just trying to sell their stuff, I don't understand why someone would react by yelling and getting angry.
You're describing routine purchases in (perhaps) a market in West Africa, probably with few tourists around. The hawkers aren't making any money from dishonest sales to tourists, and sales are probably reasonably consistent. Repeat customers are common.
The others are describing very popular tourist areas in poorer parts of Europe. All their money comes from tourists, sales rise and fall frequently, there are no repeat customers, and there is strong competition between hawkers for the best places, and possibly efforts to keep newcomers out of the trade.
So does spam. That's why spammers keep sending it.
Does that mean it's OK? Clearly not.
Out of curiosity, if they weren't trying to sell you anything, but were behaving like that (hissing/kissing/blocking your path), do you think getting angry would then be an appropriate response?
In that case what you're doing seems to be significantly worse than saying "fuck off".
Maliciously wasting their time vs making it clear you aren't interested?
FWIW, I don't think there's anything wrong with what you're doing. I just think it's objectively worse than "yelling and getting angry".