I've had great luck finding used camera gear on KEH.com. Their ratings are conservative and everything I've bought from them has been exactly as described or better. Definitely worth checking to see if they have any used Sony FX3 cameras in stock.

Have you checked B&H Photo Video Used Store ? I bought a used A7siii for $2000 in late 2023, works well until now, no issues found.

Adorama used store also have some great deals on used FX3.

KEH or MPB are currently top rated stores for shopping used cameras and lenses. Both have 6 months warranty for all used items.

KEH, they have 180-day warranty.

The best places to buy a used Sony FX3 include reputable online marketplaces such as B&H Photo Video and Adorama, which often have certified used gear with warranties. KEH and MPB are also excellent options, specializing in used camera equipment and offering detailed condition reports. Additionally, eBay can be a good choice if you're cautious about seller ratings and product descriptions, while local camera stores may offer hands-on inspection opportunities and in-person purchasing.

KEH.

I bought a used FX3 last week at MPB. Like a new one.

I bought one at MPB.