nah - literally people are attracted to even round numbers and 25 intervals. The 99 also works. It's why supermarkets use em.
I see the same drop by 1 post after I make 10-25 k off the same card after 5 sales all the time.All in a few minutes.
Read "Propaganda" Edward Bernays - doesn't teach this particularly but modern advertising in general. Basically, how people are programmed to think. It's how everything is sold since the 40/50's.
Not saying the drop by one people can't make stubs. But attractive numbers get quicker movement is it.
And often you can bid war and drop back to just before the bid war gets too far... and they'll lose out and you can gain a couple k by a quick back off if it's just two.
a bit of trolling into someone into going to far - but not for someone putting in 10-20 bids then actually playing a game then going back.