You will always win a bid by 1 gold.
Let's say I bid 100 gold. If no one else bids, I win by paying 1 gold.
If someone bids 5 gold, since I already bid 100 gold earlier, I will still be the highest bidder by 1 gold, so the top bid (mine) will be 6 gold.
If someone else bids 200 gold, they become the top bidder, but again they only win by going 1 gold over my total. So if they win they pay 101 gold.