You have to ingrate EasyPost API into your product! It will make Sellacious so much better and easier to ship the items for sellers. EasyPost supports over 100 shipping carriers around the world, their API is very easy, and requires only a few lines of codes.
EasyPost plugin would be great for Europe and US markets. EasyPost is not free, they charge 0.1 cent for each shipping label, however they give a discounted rates. So you actually save money by using their sevice instead of buying shipping labels directly.
If you can integrate this service into Sellacious orders page, this would make the life so much easier. Right now in order to ship a physical product, I have to go to USPS carrier website, then go back to Sellacious orders, copy the order address, go back to USPS website, enter the address, create shipping label. Then go back to Sellacious, enter tracking information. Very time consuming. This ingeration would definitely help and save time.