They lowered the price on the flagship unit a few months ago by a couple hundred bucks and this might be a new discounted unit from a dealer that is tired of looking at the thing in stock...if it is not an older unit that is pre DST without the upgrades.
Before they lowered the price they came out with the Anniversary Edition minus boost and cache but with DST and the other upgrades for $600 but most dealers discount that one to $499.
Pretty much shooting themselves in the foot when they did that because that one was sure to pull sales from the $1000 flagship and I assume it has.
FTP isn't stupid and I am sure they knew this would happen but they made other moves lately like discontinuing the $679 F70 and rebranding it as the Patriot at $400, moved a few models over to the Teknetics brand too and so it sure looks to me like they are reconfiguring their lines plus making room at the top for new models in the Fisher line.
Rumors are there are new designs in the pipeline under development, multi frequency, a new PI unit and who knows what else.
They won't say anything till they are close to releasing any new models but I was in retail for a long time and in my experience companies don't make major moves like this, coming out with cheaper top shelf products, releasing cheap close to full featured models and all of a sudden discounting long top selling full featured popular flagship units unless they are working on some sort of long range plan...we just don't know what it is yet.
There are a ton of dealers selling all flavors and versions of the F75 models on Amazon so it pays to be careful.
If this is a full blown top of the line new F75 with DST, cache, boost and everything else from a known good dealer it is a bit unusual but possible...if this dealer doesn't care that FTP will probably pull their dealership for selling a new flagship unit at this price.
if it is the 85th Anniversary edition that one can be found cheaper.
If it is a pre DST LTD unit that is just old stock and some may bite but in my mind not worth it with the other choices available.