You can, but you also have to remember that buying coins off e bay is like searching for buried treasure in shark infested waters. For sure, there are bargains to be had, but you need to be experienced in working e bay auctions to best advantage, as well as really knowing your area of interest, such that it becomes an area of expertise. Not to mention possessing an ability to accurately discern grading from often poor photography.
I reckon I can do it now, but it's taken 10 years of trial and error, and several occasions of getting my fingers burned, to get there. Good luck