I’ve bought and sold a couple different ways:
Purchased a PJ Delgrange (like new) from eBay, but was very confident it would fit the horse it was being purchased for.
Purchased a Tad Coffin A5G2 from Horse Clicks - had to send one back as the panels were pretty beaten up. Second one was great…and sold it in the barn and then sold it for that person a few years later via Horse Clicks - no issues
Bought a low end, low priced Zaldi Star on eBay, sold it 10 years later via FB local group for a bit more than I had paid for it. That was a factor of the very low eBay price, though.
Just bought a CWD SEO1 from FB - but I was also very confident it would fit the horse because it’s the same that his owner has. No problems with the purchase.
All have been great purchases - including the PJ when the seller accidentally refunded my PayPal and we had to figure that out…