I am surprised that you find there are more 3/4 than 4/4 violins on ebay. It's really the contrary. there are tons of full size violins for sell everywhere on the web, and as many in local dealers. Why use a 3/4 too small for an adult if you want to learn? it's already difficult with an instrument of the proper dimensions relative to your body that there is no need really to make it even more complicated with a too small one....