Finding what you want, and getting as good a deal as possible, are pretty much mutually exclusive.
If you are there early on the first day, you'll have the best selection, and you can grab anything you're after before someone else snags it, but you likely won't have much bargaining power.
If you are there late on the last day, you'll have the best bargaining power, but the selection won't be very good, and what you're looking for has probably already been snatched up.
If there is something specific I'm looking for, I go early.
If I am just looking for a bargain, I go late.
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