> I get service, can they simply check for bad alignment and just charge for that If the alignment

You can often tell by how the tires are wearing and how the car drives. In theory the "correct" alignment for your car should cause your tires to wear evenly, and when you drive down the road on a flat, level, smooth road, and you let go of the wheel, it goes straight, or maybe drifts a hair to the right. It should not drift to the left.

If the side towards the center of the car is wearing faster then the outside, or other way around, it means the tires aren't "flat" on the ground.

The point of having your alignment done is to make sure the tires wear evenly, the car drives straight easily.

A car gets out of alignment by parts getting slightly bent. Even thick steel parts will slowly bend over time. And alignment is measured in 0.1degree increments. So just a hair off will make your car drive less smoothly. They measure it in 2 directions, plus the difference between the right and left side.

I had an old truck that was off 4 or 5 degrees. It still drove, just... you just had to keep your hand on the wheel to prevent it from turning right. It wanted to turn right, and went through tires quickly.