You are, of course, supposed to sell the item for the highest price unless it hasn't met the reserve.
However, I haven't yet heard of anyone taking a seller to court for breach of contract, but you would get appropriate negative feedback.
You have four choices:
Start at a low price to attract bidders and hope it flies. Most bids come in during the last minute or so;
Start at the least you are prepared to sell for;
Start with a low bid and put a reserve price;
Start with a low bid a high 'buy it now' price, also with a reserve