I disagree with many who have previously posted, but I trust PSA/DNA and only PSA/DNA to certify autographed baseballs. Some of the other companies in this industry are trusted, but if you look at realized and completed prices on eBay you'll see a higher premium paid for items with PSA/DNA certification.

I buy quite a few uncertified baseballs on eBay myself, and funny thing is Ken aka earlywynnfan is one of the few people I see list baseballs uncertified and he gets good prices for them. Quite a reputation he has. Most other sellers do not get premiums for genuine balls as the public is getting smarter and smarted these days to fraud and misrepresentation.