The person who is currently the highest bidder has a bid in that is higher than what you're putting in. So say they bid 1500, it will only charge them what the next highest bidder put in. So you put in 705, their bid is still higher than yours and will charge them 707 until you come in higher than their 1500 (arbitrary number, I don't actually know what it is). Does that make sense? It's kind of hard to explain.