I think it’s far more common for devices to get pairing wrong than to get it right.

Just a few of the very common issues I’ve seen in various devices:

• TVs that are constantly in discoverable mode, even when the screen is off. Just in case the owner loses their remote and wants to pair a new one without reaching behind the TV to press a button. No way of avoiding this except disabling Bluetooth entirely, which makes the stock remote lose either partial or all functionality. Pairing requests also interrupt whatever you’re watching.
• Audio devices that have a very short delay after turning on and waiting for any already-paired devices to connect before switching over to a pairing mode instead. So short that a smartphone in a low-power state (e.g. because you haven’t unlocked it for a few minutes) might not connect in time. Most if not all of the bluetooth-to-3.5mm receivers intended for older cars seem to share this problem.
• Pairing codes are extremely underused in general, even among input devices. Most things seem to just pair with whoever sends a request first unconditionally.