To Bee and Richard:
Sometimes digital files are customised with personal info after the purchase- by the seller. The listing is listed as digital download, but client really pays for the services, and specific customisations, not for a ready to print file.
That is why we sometimes need to transfer files outside of Etsy, because there is no way to initialise a transfer after the purchase. Also, professional print ready files are usually too large for Etsy system.
To Alicia:
I only had one sale here so far, and so am not sure what is the best system, but I noticed straight away loss of quality in images uploaded via etsy convo.
It looks like it is only good for proofing, as messaging program is formatting images and optimising the files for web view. That is not good for print for sure.
I used email instead. I think it is pretty safe. There is also service called We Transfer that is helpful in sending large files.