It is better to order a small amount. I usually order ten of two different kinds, for a total of twenty seed. If I like the seeds, I separate a male and try to get some more through selective pollination. Or, if the strain is real bushy, as soon as the gender is identified, I take a long six inch cutting and start a mother plant. The mother plant might be able to give you good clones just about the time your original seeds are matured and harvested. This is why I prefer regular non-auto seeds, and why I don't like the feminized too much. You can get clones from feminized, but getting a bunch of seeds is harder to do. If you do it this way, you don't have to order very often. Depending on my luck with getting a good strain, I might not order but once every year or so. As long as you have a few of the regular seeds, you can replenish your seed stock at a future date. This is why I don't like feminized.
BTW, I think the amount that gets snagged by customs is pretty small. You would think they would focus on real serious problems like someone ordering vicodin from India.