If I'm not mistaken, the current minimum bid increase seems to be a mere 1% of the previous bid; this is incredibly problematic for the following reasons:

Bids are currently decided NOT by who is willing to pay the most, but simply by who is willing to sit around at the auction house for the longest period of time, instantly outbidding their competition by a couple of crowns at a time.

This encourages players to spend all day loitering around the auction house. It severely punishes players for actually stepping away from the auction house and PLAYING the game, or logging off for any amount of time, as they are guaranteed to be outbid the minute they walk away from the auction house and have no way of bidding until they have exited the dungeon and returned to the auction house.

The insignificant bid increase margin also negatively affects an auctioner's potential profits, as even the most competitive bidding wars will only cause the current highest bid to crawl upwards at a rate of a couple crowns per minute.

Outbidding the competition by such small amounts at a time, and so very frequently, results in mass quantities of Mail spam that has to be cleared out to recover surpassed bid money. This is just plain annoying.

The only way to give yourself even the slightest chance of outbidding someone camping an auction a few crowns at a time is to raise your bid by an unnecessarily large margin over the previous bid, in the hopes of scaring away the nickel-and-dime-bid-spammers. While this would at first seem like a good thing for the auctioner's profits, it can EASILY be turned into a con-game: the auctioner merely has to have a friend constantly opposing bids by a couple crowns at a time until a REAL bidder becomes desperate and bids far more than they normally would.

Raising the minimum bid increase amount to 10% would make bidding go much faster, as the bids would quickly climb up to the level where bidders actually have to consider whether it is worth it to bid higher or not, as they will have to outbid by hundreds of crowns instead of tens. At this point the auction-campers might actually consider PLAYING the game; there will be no need for them to ninja the auction further because they've either reached the point where they aren't willing to bid more, or they have the highest bid and some measure of confidence that they might actually win even if they step away for a minute. This eliminates the potential scam of ninja-bidding friends' auctions to pressure people into bidding too much by introducing a real risk that someone WON'T try to outbid the scammer, leaving them receiving their friend's item while they suffer a net loss of the sale tax.

Additional, separate auction house improvements that I feel are essential, with or without an increase to the minimum bid margin:

There must be an option to place a bid directly from the piece of mail recieved informing the player that they've been outbid. Sending this kind of notice to a player in the middle of a dungeon without any means for them to DO anything about it until it's too late amounts to little more than insulting the player. "Hey, you're losing this auction and there's nothing you can do about it!"

Additionally, the remaining time on an auction should NOT EVER be seen by the bidders. The current system encourages people to completely ignore an auction until they are sure it is nearly over, and then try to ninja it for the bare minimum price. The most desirable items will ALWAYS go for their buy-now price, making bidding pointless, while less desirable items will go for only the bare minimum, a kick in the face to the auctioner who will either make no profit, or LOSE money depending on how high they set the initial minimum bid. THIS in turn has ensured that ONLY the most popular types of items even show up in the auction house in the first place, leaving less-appreciated items (such as the recipe for any bomb outside of the haze series) of a nearly mythical rarity outside of Basil's shop, which defeats the intended purpose of an auction house making it easier to acquire items.

TL;DR Summary:

Minimum bid increase must be 10% higher than previous build.
There needs to be a way to increase bids while away from the auction house itself.
Bidders should not know how much time is left in an auction, while Auctioners should see a more precise countdown.