I tend to use "they" because I am bad with names. A lot more people are bad with names than are trans, or have nonstandard pronouns. If I can't remember whether your name is Lynn or Leslie, I am probably also not going to remember whether you are he, or she, or they, especially if it's not visually obvious, or if it contradicts the usual expectation.

If people are upset with being misgendered, well, that's unfortunate, but they're also going to be mis-named despite my best efforts otherwise. (Not deadnamed. That would require me to remember their name! Ha! Fat chance!)

So if you can remember names and pronouns--good for you! However, if you (generic you) think it's misgendering to be called "they", well, that just might be rather ableist of you.

There are really only two choices here that can work given the presence of significant numbers of people who forget names: he/she, and don't worry about it if it comes out wrong; and they, and don't worry about it.