I've been a casual user of Ebay for about 20 years but this was new to me! I was watching a couple of 'buy it now' items and the sellers messaged to offer a lower price. It said the offer had also been sent to other Watchers so first come, first served, I guess.
Just thought it was worth highlighting, and wondered how long this had been a thing! (I'm aware buyers can 'make offers' on BIN items they want to buy, btw). A quick google suggests it was brought in last year. Worth keeping an eye on your ebay messages if you're watching stuff...