I don't understand the buying attitude of those bidding

ANY HELP IN THIS MATTER WOULD BE WELL RECEIVED THANK YOU.  bILL

I think you will find that the majority of buyers will always want to try and buy at the best possible price. The reserve price on a listing is the lowest price the seller is happy to sell for, so anything above that is a bonus as far as the seller goes. I don't imagine any sellers would be selling anything with a mark up as low as 50%. Think about the maths.

Forgetting any delivery costs, buy something $100, sell for $150. From that $150, Trademe get a success fee of around $15, the seller may have paid extra promotion fees says 2 lots of $3.95 = $7.90, so now that $150 sale has reduced to $127. If the seller is GST registered, 15% of the $150 is $22.50, so that leaves the seller $4.50 margin on a $100 cost item. Tax and everything else will leave the seller out of pocket and out of business.

If you are selling and receiving offers that are too low and below your reserve, just reply, sorry, the reserve price is the lowest I can go.

Just set a reserve for a price you will be happy with that way no-one is unhappy.  Unfortunately its not the buyers fault if a seller sets the price too cheap (if it was a bad accident like a typo error that's another can of worms).  Once an item is sold, the new owner can do what they like with it really so just cover yourself by only listing it for a price you are prepared to sell the item for.  The upside to selling on Trademe rather than Ebay is the shipping costs are much lower for the buyer since most buyers on Ebay are overseas so local buyers may bid more for the item since the majority of buyers will also take the shipping costs into account when bidding.  Also bear in mind, selling on Ebay you may have to consider export fees / custom clearance for certain values if sending overseas so would need to check NZ Customs website so you don't get any unexpected fees, no need to bother with that if selling local on Trademe.

As above as S  stated, set your price you are happy with,

Once you have sold something, It is no longer yours, The new buyer can do what they like with item ,

which means they can also resell it, if they got it cheap to make more money,

This is what auction sites are all about, buying peoples 2nd hand Junk / unwanted items,

and reselling them if they know they are more valuable than they paid them for,

This is why people scour garage sales, op shops etc, looking for those treasures they know they can move on

and make some money,

As they say one mans Junk is another mans treasure,

So even if you go to E-Bay, the same will happen there, there will be buyers, purely buying to resell at a higher price,

if they know they can make some money,

Apart from all the other comments so far, which I agree with, you might need to get realistic about valuations for jewellery.

The valuation is largely an "insurance value" These are always in my experience far in excess of their "market value." People tend to get excited about a valuation of their jewellery and quickly come back to earth when they realise the market value is much lower. When I was looking for engagement rings many moons ago, items with a valuation of around $5k had a sale value of more like $1k.

Unless you happen to get a "I must have that at whatever cost" buyer come along, I think you will find your $1600 valued item has a more realistic sale value of $400 -$500 or so.

I dont understand why some people get upset over someone bidding on an auction with the intent to resell the goods. Thats what I do, its my full time living to sell on trade me using this method. I buy items in bulk, clean them, (many times the arrives arrive in bad condition, yuck!) Research how much each individual item is worth, take photos and list on trade me. I do this 8 hours a day, every day as im a disabled woman who has to work from home. I recently came across another resellers trade me page - one of their feedbacks was from a seller who was angry that the buyer bought the goods with the intent to resell them. So far no one I have bought from has told me they weren't happy with me reselling. If a person wants to get rid of an item, why do they care what the buyer does with the goods? Its no longer theirs? If the seller is upset because they realise the item is worth more then they got for it, then why doesn't the seller list the item themselves for that price?

And most of the time, when selling an item on trade me, you will not get RRP for it. Especially with clothing and jewellery. You can list the piece at full RRP, but you should not expect to sell it within a week. Or even within a month. For such an expensive item, you really need to wait for the right buyer to come along. So the question comes down to, do you wanna make a quick sale but get less for the item, or do you want full RRP but wait a while for the item to sell?