I guess it depends on your definitions of 'complicated' and 'not being able'..
In my experience, people often expect the unknown to be difficult and unless they ever try it out for themselves, this belief will stick with them for life. That is why you sometimes see sales with terms like 'US buyers only' or 'Only for sale in the EU'.
Additionally, some people have had negative experiences with customs etc. and so prefer to keep the sale of weapons within their own zone.
Although one could certainly suspect sinister motives, perhaps your seller is simply unfamiliar with intl. shipping and forgot to state it in his terms?
The best way to find out would probably be to talk the guy...?
Hope you work it out, - Thor