Unless you whack potholes, got into accident etc, your camber would not go out of alignment easily.

The tyre shop that I go to, will have different camber reading, even when done back to back. But the toe readings are consistent. That means their machine is not well calibrated for camber. But for that's OK because the shop never asked me to adjust my camber. He says as long as the tire wears evenly it should be fine.

If a shop is unwilling to do toe adjustments if they don't adjust cambers, I'd go to another shop.