I've bought firearms off the internet numerous times, and only had one problem transaction. You guessed it--Impact Guns!!!
I placed an order for a FN Tactical shotgun. The website said if it was out of stock, that they would notify me immediately. I paid for it, and sent an FFL copy. After hearing nothing for weeks, I tried to contact them to no avail. The website says to contact them via e-mail only, which I did originally. Then I stated calling. Every time, I would get a stupid answering system message telling me to e-mail them, or to enter my party's extension number. Finally, after about the 10th call, I just typed in some numbers. Someone answered and I told them that I had the wrong extension and needed to be transferred to someone about a current order. I was transferred to someone who said that the shotgun was on backorder and they didn't know when it would be in stock. I promptly told them to cancel my order, and bought a Benelli M1014 shotgun locally the same day.