I really admire Dallas Brett. He listed loadable dumbbells at $500 and specifically noted firm on price. I have no problem with that. Facebook Marketplace is a resource for everyone to use. A week later, he drops the price to $475 as if that 5% drop will bring in all of the buyers.
As an aside, these do retail for $650 and in my opinion have a very limited market. It was not unreasonable to get 75% of retail during the crazy sellers market. They are in like new condition. The fitness market is starting to become a buyers market. Loadable dumbbells are cost effective compared to fixed weight dumbbells, but in my opinion clunky to work with and certainly not as secure.
I have seen Fringe Sport DB handles and Titan DB handles for around $100 for a pair.
I personally own a cheap pair of CAP loadable handles that were purchased for $20 (with 40# of weight plates) with the specific intent of using them for one arm dumbbell deadlift. I load them with full size (18") plates and would not use them for much else. I would also like to build out an inch dumbbell.
Unfortunately the inch replica handle by FBBC is discontinued. For my purposes a fat gripz handle ona a standard dumbbell is more than sufficient.