GunBroker.com has done to online sales what Rush Limbaugh has done to Talk Radio; revolutionized it! Even if you just want to find out what the going price is for a particular model, GB is great.
My three best deals; NIB M85 for $206, PT100 for $235, and Rem 1100 12ga for $349. But you are right, the great deals are getting much harder to find.Always pay with credit card or USPS money order. I have scored some sweet deal on there but they are far and few between. Plus I would only deal with someone that has a phone number included.
As with all things online you are taking a risk but when done right you can keep it minimized.
Best deal: PT1911 used blued for $315 shipped plus the $30 FFL but that was in 2011