This seems a bit disingenuous. If you know you always tip a dollar for a coffee (not hard for a lot of people on Hacker News), you can simply mentally add a dollar to the listed price. (also not hard for a lot of people on Hacker News)
How is this a personality test? Just price in the tip exactly like you would for going out to a restaurant.
No, your point was not lost; in fact, what you said is exactly what's so grating about "guilt tipping."
Think of it in terms of privacy. Whether I can afford to pay $1 or $5 or $50 for a cup of coffee is none of your business. I don't care if I'm destitute or a serial Powerball winner.
Suppose you stood next to a Starbucks cash register. As each person reaches the front of the line, you announce "you look like the kind of person who can pay more," or "yikes, you can barely afford that lemon-twist chai, here let me press the no-tip button for you." Can you imagine how you are making those people feel? No customer wins in that scenario.
Yes, buying coffee should be "trivial." Now it's been elevated, by design, to a public shaming.
I’d like to point out that restaurants can customize the default pct amounts to tip, and it’s a hassle in the moment to click “custom” then type in either a dollar amount, or your own percentage, whichever the POS system is designed to show. (Lately some places set the options to 20% as the minimum, as the article says) You don’t know what you’re going to get. The server can tell if you’ve tapped “custom” because it’s 3 or 4 extra button presses, whereas the default amount is one tap.
> they want to know the posted price, so that they can decide to buy or not
It's trivial to know the price of the coffee with tip: you just add one dollar. To make it sound like this is task is so difficult OP would sooner not buy a coffee seems disingenuous to me.
For your convenience, I've included the top two definitions of "disingenuous" below. I think the second one is particularly apt.
1. Not straightforward or candid; insincere or calculating.
2. Pretending to be unaware or unsophisticated; faux-naïf.
How is this a personality test? Just price in the tip exactly like you would for going out to a restaurant.