I looked over the two auctions. The $100 one can be seen via this link:
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?MfcISAPICommand=ViewItem&item=214030961

The first thing that strikes you is that both the buyer and the seller have ZERO feedback. Clicking their eBay ID, I found that both are in eBay for less than a month -- one joinedNov 15, 1999; the other, Dec 5, 1999.

Then I went to the eBay
Contact Info. page (http://cgi3.ebay.com/aw-cgi/eBayISAPI.dll?MemberSearchShow) to find out where they lived. If both live in the same town, it is very suspicious of shill bidding. Here one lives in Los Angeles CA, and the other lives in Ramona CA -- looking at a map, it looks to be 50 miles apart.

Like always we can't be sure of shill bidding just from this.