Ebay is hit or miss. I used to bid on items right away if I saw them, but that just drew attention to the auction early, and as stated above, causes the record to probably close at a higher price. Now I just put the item in my "watch list" and ebay sends a email when your "watched" item is winding down, then I make a bid if it is still within my means.
All in all, I personally like ebay because I know what records I want and how much I want to spend.
I recently picked up Bunny Lie Lie/Lee Van Cliff "Who Cork the Dance" (JB Music 12") for under 5 pounds
and "Five Man Army" (Oak Sound 12") for under 7 pounds, so the deals are there, you just have to be patient and not get into a "One Up" war once the auction passes your mark.
One love and good luck digging!!