I want to get a personal copy of Visio 2019 for home use. I don't understand why prices vary so much between shops and within eBay. Below are examples of the same thing - Visio Pro 2019, 1 PC, no expiry
$478 Officeworks
$439 eBay, retail box
$199 Software Giants
$80 eBay, from "certified partner"
$40 Amazon au
$7 eBay, seller feedback score 21
Which one should I go for?
Stores like Officeworks are going to be selling you the genuine intended for retail versions of Visio. The much cheaper dodgy eBay stores are going to sell you Visio they've purchased in bulk through Volume licensing for a low price.
Reselling VL/MDSN etc. is a real grey area and there is the risk of your key no longer working, but that rarely happens. Being a Gold partner I'm licensed to 5 copies of Visio Pro that I could easily resell. Or I could buy a few dozen in my Volume License portal and resell those too.
Alternatively there is Visio for O365 at $6.90/mo or $20.60/mo. There is more info on Visio versions here