I think you are complaining about multiple issues here.
1. You didn't like the quality of the pump, it was not fit for purpose.
2. You felt the seller was dodgy, advertising an item as in Sydney but sending from somewhere else.
3. It was not sent all that quickly, it took them a week to even post it.
4. It did not arrive at your home yet (maybe tracking?) showed it as delivered and seller told you to check if someone else in the house had taken delivery or if it had gone to a neighbour's house and you feel that is not your problem.
The trouble here is we have no idea what you complained about to ebay.
So llet's have a look at each issue.
Fact is, all that matters to ebay is that an item is delivered and delivered in the time frame as advertised.
If the seller achieved that, then ebay will not care too much about points 2&3.
In fact if tracking shows it as delivered, ebay may take the seller's side on point 4 as well.
So that leaves point 1. And when you think about it, that is the main problem anyway, isn't it? That you have a faulty product.
So you need to focus on the main issue, don't wander off onto other tangents.
You don't need to report anything at this stage: Open a proper ebay claim for item not as described, faulty. Open it immediately, don't bother trying to sort it out with the seller. The seller has no control over you here, you can open a claim with ebay.
Once you do that, the seller will need to issue a return postage label (if they want the pump back) and you will get a full refund. Ebay will force it from the seller. Keep an eye on the claim and don't let it time out, follow it up. Accept no offers of a replacement (which would likely be of the same low quality anyway) and no offers of a partial refund etc.
Then you can give appropriate feedback.
Sellers who misrepresent item location are absolutely rife on ebay, ebay seems fine with it most times. In your case, it sounds like Chinese stock that is drop shipped or kept in warehouses in Melb & Sydney.
Ebay doesn't care about how long you've been on ebay, there are rarely any humans monitoring things anyway, so just open your claim, get your money back.
