The third weekend in July, the third weekend in July, the third weekend in July. It's the mantra for Greater Cleveland bargain-hunters. That's the weekend that friendly Avon residents fling open their garage doors, prepared to liquidate those off-the-mark gifts or later-regretted purchases from the previous year. There are so many garage and yard sales that shoppers really would have to use the whole two days to see everything. And prowling around every sale is the real goal for buyers who don't want to miss the mother lode of great stuff. After all, one man's junk is, well, you know.