I ordered twice on HSN for items that were not available in stores, or came with a really good deal. The shipping and handling charge is up front so there are no surprises. The items are delivered very well packaged.
You can call even after the show has aired, as long as you have the item number available and it's still in stock.
Another time I had ordered something but was able to cancel it without a problem.
You need to be aware of the prices as compared to what you can get at a store using a discount coupon, which can often be cheaper than the TV price.