Why did my auto bid jump

Somebody else came along and saw your bid of $51, then they put in an autobid that conicidentally equalled your autobid. Since you got there first, yours is the bid that stays and they miss out.

Probably another Trade Me "feature" that's not intuitive, but it's been explained in the help section:

https://help.trademe.co.nz/hc/en-us/articles/360007263411-Placing-a-bid

Auto-bid used to be buyer friendly and only jump by the minimum increase. Now it goes straight to the maximum value. This is an unacceptable change that is catching buyers out and causing us to pay far more for items than we should be. This is just greedy on behalf on Trade Me and clearly designed simply to maximise fees. 

I made an auto bind on a trailer that was at $580 at the time., The reserve had been met. so I put on my auto bid. there were no further bids. The auction went straight to my maximum of $1010.

the answer is dont use autobid, I put an autobid on 123.60 and what do you know it jumped straight to that from 102.00.  amazing!  Best you sit and put your $1 bids on.  Its a rort!

I just had a similar experience. It seems that the system is broken or they are just stealing. I would like to see the digital proof that someone else setup an autobid, or I would like them to honor the lower bid.

Hi Clinton, thanks for posting. The system is not broken or stealing from you, and you set up the auto bid correctly. The auto bid did what you asked it to and made sure the item was secured for you.

I've gone and had a look at your recent auction win and the auto bid was doing just as it should've. You stayed ahead of the bidding war with the other member - their bids against you show on the history since they were in different amounts and remained under your maximum. The digital proof that a bid (either an auto or manual bid) that equaled your maximum was then placed is right there on the bidding history: where you see your bid of $51 followed immediately by your maximum bid of $60. That is the proof. It isn't possible to have 2 bids placed by 2 different members in the same amount, so from the 2 final bids being from you, we can see that a competing bid was entered in the amount that required your auto bid to max out. 

Hi Lucy, can you explain why my auto bid went from adding $1 to $5 please and why?

Kia ora T. When the leading bid gets to between $200 and $1,000 on any auction, the minimum bid increment is $5. You can read about that here.

Your maximum autobid was over $200 so when the auction got to that amount, that new increment kicked in.