i think it does not matter wich online sale system you are working with.
etsy, ebay, amazon ... and so on a nd on...
there will be allways some people who can not figer how to and there are those people who do not want to join something if they found you over the search engine a nd just want to buy something quick and easy.
if we loose buyers? well, we never know but it is just too stressfull to spend too much time in think about that, you could even habe an brick and mortr store and probably could lose sales because you are on the wrong site of the street.
what we do not have we can not lose, but we can help if they let us know and being paciente w ith them. that works pretty well.
i had some people who did not wanted to join, i sold like
foxgloveaccessories with sending invoice over paypal. it worked.