I can tell you my experience with exporting to US with Irunguns, I send my 50 BMG to Irunguns to hold in Arizona and I was going to sell through it, make sure you get everything down on paper because when they received the rifle in the US, the rules started to change, fees started that I was not told about, also for them to sell your firearms they will either charge 10% of sold value or if you want to sell it yourself they charges fees which is fine if you knew that prior to shipping it down there because you can never bring it back, they have total control.
I actually have no problems with them selling it and charging a fee, but the fee needs to be appropriate. If they sell a rifle for 1000 they charge 10%, but in my case the 10,000 rifle they will charge the same 10% and it is the same cost to them to sell a 1000 rifle as a 10,000 rifle. This is above the fee that Gunbroker also charges, also they charge you transfer fee and shipping fee and packing fee to the FFL they shipped the gun too.
In my case I sold the firearm myself quickly, and the guy who bought the rifle had contacted me off Gunbroker because the rifle has a 3 year waiting list to buy a new one and he thought the rifle would sell for higher than the initial price I had it list for, so I did not have to pay them a fee and he picked it up from them and he was a FFL so I only had to pay a transfer fee and a month storage. Am I telling you not to do this, no, but get everything down on paper to know what your are getting yourself into, now I paid 10,500 Canadian for the rifle and sold it for 10,000 US minus the Irunguns fee so I did quite well on this.
I would do this again but this time I would negotiate all fees and have a contract with them. I like Irunguns and have bought severasl guns from them and imported rifles from the US to Canada from them and will continue, but this one transaction really bother me at the time because I felt I was being taken advantage of