eBay is a great study on human behavior. If everyone behaved rationally, according to the same set of "rules" then the outcomes would be totally predictable. The lack of predictability is a good indicator of the lack of rationality among the bidders, and/or an indication that people make decisions by different rules.
If everyone who saw that uke thought to themselves, "The most I'm willing to pay is X" and then went ahead and placed a bid for X, the process would be very straightforward and everyone would end up "happy" - either, you won for less than X - which is great, you "saved" money. Or you won for X - you paid the most you were willing to pay, still a happy ending. Or, you lost because someone outbid you - in which case you are happy because you didn't overpay.
The problem is, many people either don't really know what their X is ahead of time, or they get emotional and change their mind because they're angry that someone bid X + 1, or they do have an X in mind but they think that they can come up with a complicated strategy to increase their chances of paying less than X, even though they are actually willing to pay X...
So - you have a choice to make. Choose your X, place a bid for X, and see what happens. Or - try to predict how others will behave (the three options in the last paragraph, or something else) and build a strategy based on that prediction. But I think, personally, that it's a bit of folly to try to predict how other people will behave, and for every strategy someone comes up with, there will be a bidder on eBay who doesn't behave in a way that allows that strategy to succeed...