[swarmee]

1) It's not normally the consignment company: it's the owners of the cards or their friends.
2) Say the current bid is $25 and you set your max bid at $101.44 . eBay will continue to bump your bid to the highest for any bid up to your max. So if the owner of the card bids $50, yours will show $51. Then they bid $60, you bid $61, etc. But if they bid $100, and the minimum increment (additional bid amount) is like $2.50, your $101.44 bid will now show. Then they stop bidding.
3) This is why people don't bid large numbers until a few seconds before the auction ends; this is called a snipe bid. It makes it harder for you to be shill bid if you bid your number only at the end.