Starting at the reserve can spook some bidders and make it hard to start the auction. Starting below the reserve usually gets some momentum going in the bidding, and that tends to carry over to a higher final price.
Advertising a price that's below the reserve is pretty unethical, though it's not illegal (the seller is never locked into a price). People end up wasting time and money (getting reports) for houses that were never actually in their price range in the first place.
