I'm looking at an FT-847 and looking at reviews. it seems like a cool radio with interesting features like satellite. any knowledge of that radio? (I'm just scouring QRZ and eHam for reviews.
The FT-847 has been out of production now for at least 15 years that I know. So consider them classics and approach one with the expectation that you need to either test for functionality or assume you may need to do repairs.
Common failures will be the power amp finals. It was based on the Mitsubishi 2SC3102 (VHF/UHF) and 2SC5125 (HF) which the FT-857 and FT-897 both use, too. These are AFAIK obsolete now so repairing them is getting more difficult.
The front LCD display on the FT-847 was a common failure. It's huge, easily damaged and prone to issues.
Also they have a susceptibility to power being reversed. Most radios, the FT-847 included, have a reverse power shunt diode that attempts to blow the fuse before damage occurs. This usually takes out the shunt diode, which is to be expected, but the FT-847 power supplies can still be damaged before this happens. It's not as I understand it necessarily super serious but will repair a soldering iron and some rework.
The main problem with them is Collins discontinued the mechanical filters used as upgrades. So installing better filters is now an eBay experience and you'll pay dearly for them. I have a 2KHz Collins/INRAD in my FT-857 for SSB and wish I'd have ponied up for a 500Hz when they were still available. Having a very narrow filter is necessary for CW (Morse) and handy for some digital modes (RTTY, Winmor, etc.).
If you can find a nice one the FT-847 is a neat radio and does a lot. Kind of like a dual VFO FT-857/897 or IOW like having two of them in one chassis. It was intended for working satellites but as an HF rig it's acceptable. Similar performance to other entry and mid grade Yaesu of the day, more than sufficient for normal users. Won't be great in a contest and doesn't have a ton of ability to filter and quiet noise, so don't expect miracles.
tl;dr
Neat radio, test if you can before buying. I'd happily put one in my shack if it was in good shape.