Just not many shows in my area to start with, and literally no shows that have any amount of tinplate which is what I like, so when buying, I just plan on paying for shipping. I'm thankful that so many sponsors here on the site are willing to take the time to pack and ship items for me. But...if you are selling "cool stuff", your buying audience is much larger online in my humble opinion and can more than make up for any extra costs you have to absorb in shipping costs. Also, if you sell alot, we all know the most popular auction site online, but there is another place you cans ell that starts with an "E" and it's getting more popular all the time (Etsy) and the fee's there are half of the auction site.
But...when selling, I save all packing materials from items I buy, that helps alot....also while the flat rate boxes from the post office are great, but check out their website, they offer all kinds of different size boxes for free....all you need is some foam peanuts. UPS store offers I think 6 cubic feet bags of foam peanuts for 30 dollars, you can pack an awful lot of boxes with that large of a bag of peanuts! If postal Priority boxes don't work, you can go to companies like U-line or even online auction sites and get the boxes 25 or more at a time very reasonable, same with the bubblewrap. There are ways to keep the shipping costs to a minimum and the better you get at that, the less cost you have to pass on to customers... if I'm selling just one car or something of a similar size and weight, I'd spend a couple bucks at most for packing materials, and never lost an item yet (knock on wood)