That's what you think but if that was so how come some of them refuse to sell to a Canadian??? Some do it out of spite. One seller cited issues with CCs. Some only take US Postal money orders or certified cheques and you have to convince them to take your bank draft in US dollars even though they are not losing anything if it doesnt go through.
Btw, it is GB policy that unless you are in US you have to inform the seller of your intent to ship internationally. It's a poorly worded policy because it doesnt take into account the fact that all legal firearm sales have to go through an FFL dealer regardless.
As it is right now, the whole process of buying a firearm off GB is bumpy.