I've only ever sold a cage once and regretted it! I still have my first cage (well second actually, the first one went in the bin within 3 weeks as it was awful). First proper cage which was a Savic Mickey 2XL. Only 80 x 50, It was the "minimum" at the time and I fairly quickly decided it wasn't big enough for our giant Syrian. And upgraded him to a 100cm Barney cage. The Mickey 2XL base got broken during a move, but I kept the bars - and then found a Ferplast cage base in grey for only £12! Which fitted perfectly. So it got used for a couple more hamsters.
The Barney was the Syrian cage for the next two Syrians. But with Pickle, who was very shy, it wasn't working with the small doors, and the Savic Plaza was around by then so I bought a Savic Plaza and sold the Barney cage. I thought I could always buy another one if I ever wanted to ........ little did I know Brexit and a pandemic were coming along! No more cages from Germany and no more Barney. Although it is available again now and thankfully there are a lot more 100cm or larger cages to choose from now. But I did regret selling mine!
The Plazas haven't lasted as well as the Savic Mickey 2XL and the Barney. First one went rusty and had to be replaced. Second one had a disaster. My current two I've had for a few years though
Ah just remembered - I did sell one other cage - can't remember what it was called now! That 75mm x 45mm glass tank with the barred top. Got it for my first robo and hated it. It wasn't big enough and the roof was noisy and scared him - so he went in the Mickey 2XL which was slightly bigger and he loved it. It was a Skyline something or other.
I am generally a bit of a hoarder though. And whenever I've got rid of something I've missed it and wished I hadn't ha ha. Same with clothes.
But sometimes you do want a change and hamster enclosures are big to store.