Specialty coffee cafes have informal etiquette that regulars know and tourists often violate. None of this is gatekeeping; it is just the social norms of any specialized space.
Order at the bar, not from your seat
Most specialty cafes are counter service. Walking in, sitting down, and waiting for a server is the most common visitor mistake. Approach the bar, look at the menu, order. The barista will tell you to grab a seat or wait at the bar depending on what you ordered.
Do not customize beyond reason
You can absolutely modify drinks. But asking for “extra hot, half foam, three pumps of vanilla, stirred not shaken” at a specialty cafe will produce eye-rolls. Specialty cafes design their menu to highlight specific coffee preparations. Trust the menu first; modify if you must, but lightly.
Asking for sugar, milk, or oat is fine and welcomed. Asking the barista to remake a drink because you want it different is also fine if you do it once politely.
Tipping is normal in much of the world
In the US, Canada, and parts of Europe, tipping at coffee shops is expected. A dollar per drink, or 10-15% of the bill, is standard for table service or made-to-order drinks. Even for a takeaway drink, a small tip on the digital pad is the norm.
In Italy, France, and other places where tipping is not the cultural norm, it is fine to skip. Pay the menu price.
Do not ask for free wifi password before ordering
Order first, then ask. Walking in, sitting down, and asking for the wifi password before buying anything signals that you are using the cafe as a free coworking space. Some cafes will refuse the password until you have ordered.
Do not crowd around the espresso machine
The bar area where the barista is working is their workspace. Standing too close, peering over the machine, or asking detailed questions while they are pulling shots makes their job harder. If you want to talk shop, wait for a slow moment and ask.
Limit how long you camp on a single drink
If the cafe is busy and you have nursed one drink for three hours while occupying a four-person table, you are part of the problem. Order another drink, give up the table, or take your laptop somewhere else. This is not enforced rigidly in most places, but reading the room is appreciated.