The best evidence is that the shill account with a positive feedback of (1) has the following 30 day history:
Total bids overall: 455
Items bid on overall: 126
Bid activity (%) with this seller (schmitys): 72%
No one active bidder would ever be so loyal to a single seller of baseball cards --- there are simply too many on eBay.
If you file a report with eBay on these auctions, you should expect the following:
1) A call back from an eBay representative (usually within 48 hours) to get your clear, verbal explanation as to why you believe that there was shill bidding in an auction in which you participated.
2) In a case like this, it will quickly become obvious to the eBay representative that the Seller is using the (1)-rating account to bid up the auction to an effective reserve level (as noted by the previous poster). As such, if you won the auction, eBay will give you the option to either purchase the card for the winning price, or to walk away from the auction without having to face a non-paying bidder mark to your record. It's best not to pay as the Seller will be banned / suspended and you may end up with a transaction in dispute where the Seller never ships the card.
3) eBay will not inform you of the outcome of the case (privacy reasons). However, if you check the Seller again within 24 hours, you'll see that his account has either been banned or suspended.
4) eBay will turn over the evidence to the appropriate authorities and the Seller will face potential fines and / or jail time.
5) You will remain anonymous. eBay will not inform the Seller that you filed the report.
SHILL BIDDING IS A CRIME ! (DON'T SHILL !) Numerous sellers on eBay are prosecuted each year for shill bidding on their own auctions or arranging others to do so. Here's a link to just one example (there are many more):
http://www.auctionbytes.com/cab/abn/y04/m11/i09/s03