Unless I personally know the person, I will always go through a FFL transfer. The reason is that sometimes, law enforcement will go after the weapon seller - remember Columbine? That was a casual sale.

On top of that, I don't want to be held responsible for the purchaser breaking any laws. Denver and Aurora have assault weapon bans that are fruity in their own right. Both cities are nutty enough to go after the seller.

I live in Denver - I don't own any magazines that hold more than 20 rounds because it's a felony if you get caught with one. If I go to Lakewood and buy an AR-15 that comes from the factory with a 30 rd magazine, you can bet law enforcement is going to call the dealer, look at the 4473 and ask the question "You know he lived in Denver County and in the City of Denver, why did you sell him an assault weapon".

As a seller, I don't want to have that discussion. I will gladly pay $25 on the sale for the background check - it's a lot cheaper than an attorney, missed work, losing my right to vote, losing my right to own guns, losing my right to hunt and fish, etc., etc.