In the US tipping is expected and relied on to supplement the wages of wait staff at restaurants. The average "standard" has risen to now 20% several years ago. If I get good service or a friendly face, I have no problem with that tip. I now notice when the bill comes, often tipping options are listed at the top. You can choose to check a box to add either 18, 20 or 25% to the bill, and automatically calculates the total, which is quick and easier than adding it up yourself. This in no way "strong arms" you, as you can add in a lesser amount yourself, although it does subtly encourages larger tips.
That said, an unwritten rule I hear of is that you never tip owners of businesses, whether restaurants, or hairdressers, for example.
In Spain, when I leave a larger tip beyond a few small coins at any sit down meal, I always get an appreciative smile and have never noticed any embarrassing looks from the person serving me, no matter how high their wage may be from their employer.