I get a lot of emails and support requests related to these features of eBay. First, there is a misconception that eBay will accept any bid higher than the current high bid. This is not so - in order for a bid to be accepted it has to be higher for at least one increment above the current high bid. These increments change as the current high bid goes up. They are also different for different currencies and marketplaces, e.g. GBP increments on ebay.co.uk are different from the USD increments on ebay.com. I provide links to pages that explain them at the end of this blog.
The second common confusion is between current high bid and maximum bid. Users note examples of auctions where they won for less than the full increment, and ask - how is this possible, if the above is true? The answer is - bid increment rules apply to the current high bid, not maximum bid of the other bidder. An opposing bidder may be the current high bidder for the price that is lower than his/her maximum bid. In order to win, the user's bid does not have to be a full increment higher than the maximum bid, in fact it can be only a cent higher, but it has to be at least full increment higher than the current high bid.
Let's take a look at this example: You are bidding on an auction where the current high bid is $110, and the current high bidder's maximum bid (something that we don't really know at this point) is $115. eBay bid increment in this price range is $2.50. We submit a bid of $116, and since $110 + $2.50 is less than $116, eBay accepts it. Following this, since $116 is more than $115, we win this auction for less than the full bid increment.
Now imagine the same scenario, with a slight difference. You are bidding on an auction where the current high bid is $114, the current high bidder's maximum bid is the same as before, $115, and you try to submit a bid of $116, again the same amount as in the previous example. eBay refuses this, and on Gixen you see the status "BID UNDER ASKING PRICE". You are upset, yet this is completely as per eBay's bid increment rules, as $114 + $2.50 = $116.50, which is less than your maximum bid. As a result, someone wins the auction for less than your maximum bid.
Bid increment rules have been there on eBay since the beginning, and it would be interesting to know the origins of it. Why were they introduced in the first place? I honestly don't know, and it's possible that no one in eBay no longer does. It would be great to hear from some of the original eBay architects who could explain rationale for it.
All this applies regardless of how you bid, with Gixen or manually. Try to place a bid manually that's lower than current high bid + bid increment, and you will see that you are unable to. The only exception is the starting price, when there are no bids from other bidders.
This brings us to another misunderstanding and false choice - snipers vs eBay proxy bidding. Gixen (and other sniping services) do not bid incrementally or multiple times, they submit your maximum bid only once, at the auction end time. It's the eBay proxy bidding system that determines the amount needed to win. So - sniping and eBay proxy are not mutually exclusive systems, they work together when you snipe.
eBay US bid increments: https://www.ebay.com/help/buying/bidding/automatic-bidding?id=4014
eBay Canada bid increments: https://www.ebay.ca/help/buying/bidding/automatic-bidding?id=4014
eBay UK bid increments: https://www.ebay.co.uk/help/buying/bidding/automatic-bidding?id=4014
eBay Australia bid increments: https://www.ebay.com.au/help/buying/bidding/automatic-bidding?id=4014
eBay Germany bid increments: https://www.ebay.de/help/buying/bidding/automatic-bidding?id=4014
eBay France bid increments: https://www.ebay.fr/help/buying/bidding/automatic-bidding?id=4014