I've purchased two revolvers that were both in great shape (exactly as described by the sellers) and for fair prices. Both sellers were completely legit, had FFLs, and shipped the guns as soon as they received payment.
You are not likely to get a great bargain on that site because any bargains get bid up pretty well by the time the auction expires.
Read the descriptions and conditions of sale carefully, and don't be afraid to ask the sellers questions (including requests for additional pictures if warranted). Check all of their prior feedback. If they are selling "as-is", better be sure you really want it and would be willing to pay to have it fixed by a gunsmith.
You also need to be patient. It may take months for a gun that you are looking for to show up in the condition you want for a price you want to pay. Also, add guns you are interested in to your watch list, and check to see what they actually sold for. You'd be surprised how many auctions go unsold because of a too-high reserve price or starting price. Some sellers seem to relist the same $550 gun for $900 for months in a row. Guess they aren't in a hurry to sell, but are willing to wait for someone in a hurry to buy.
Watching these auctions and the sale prices will let you learn what the genuine going rate is for the guns.
Keep in mind that you'll need to add about $25-35 or more for shipping and probably $25-50 for your local FFL transfer fee. Sometimes that is offset by not having to pay sales tax unless the seller is in your state, but it's still something to consider.