That alone is not against the rules, but if they relist, eBay might see that as ending an auction early because the price wasn't high enough. If that's what happens, it's called 'Reserve Fee Avoidance'.
Sellers can cancel an auction anytime up to the final 12 hours. There are a variety of reasons someone may do this.
http://pages.ebay.ie/help/sell/end_early.html
There are some fee avoidance issues, and you can report sellers who look like they are ending auctions to avoid reserve fees. eBay doesn't police listings. eBay does read (and respond where appropriate) to filed reports. Report the violations to eBay. eBay certainly does not have a different rule book for sellers.
http://pages.ebay.ie/help/policies/listing-reserve.html
Sellers are not permitted to cancel bids and end listings early in order to avoid selling an item that did not meet the desired sale price. This is considered to be reserve fee circumvention. Although there are legitimate reasons for ending a listing early, abuse of this option will be investigated. Report the seller if you feel he violated the fee circumvention policy. You can read this eBay help page for more information, there is a link on that page for reporting to eBay.
http://pages.ebay.ie/help/policies/listing-circumventing.html
If a listing has 12 or fewer hours remaining and has, or had, a winning bid during the final 12 hours of the listing, the seller will no longer be able to end the listing, except to sell to the current high bidder on eBay. "eBay" has introduced this change recently. The policy was instated due to thousands of complaints about sellers circumventing fees by simply cancelling bids and ending auctions early in the last few minutes of the auction if they didn't like the closing price.
