There are three ways that I have been successful - 1)if the item is still active, and the seller has over priced it and I can give him a link to somewhere that validates that, he can go in and readjust the minimum bid, then I'll snipe it 2) if the item ends and is not sold, then I often ask if the seller wants to sell directly to me (I use myeBay to watch these items until they close - often the seller will, 3) if the item does not sell but the seller wishes to relist, I'll suggest a more reasonable opening bid - they don't always use it the first relisting, but on the second relisting they usually do.
I also use the ask seller a question to go over all this with them.