When I find the same witness turning up at marriages, I just put their name into the next census following the marriage and it usually turns out that the witness was the Parish Clerk.
Don't ever give up searching though, you may get a clue, from someone else. I had an instance where a young girl was listed as a visitor with my 2 x g.grandparents on a census and I couldn't work out whether she was related or not. I didn't think it was important enough to pursue, but then later I was contacted, via GenesR, by someone who thought my 2 x g.grandparents might be ancestors of him too. He had the young girl in his tree and, of course, if I'd bothered to research her, I would have found out that she was the daughter of one of my 2 x g.grandparent's granddaughter and her husband.
