How to buy real autographs eBay?

I understand that high profile celebrities autographs for low prices are probably fake but what about old forgotten musicians. I see alot of autographed items with COA of people like Johnny Mathis, air supply, chubby checker etc. people who were once big but have been forgotten an their autographs with a coa sell cheap like 20-35 dollars each. Is it likely these to are also fake?